update ceph source to reef 18.1.2

[ceph.git] / ceph / src / jaegertracing / opentelemetry-cpp / third_party / prometheus-cpp / 3rdparty / civetweb / src / third_party / duktape-1.8.0 / src-separate / duk_js_ops.c

/*
 *  Ecmascript specification algorithm and conversion helpers.
 *
 *  These helpers encapsulate the primitive Ecmascript operation
 *  semantics, and are used by the bytecode executor and the API
 *  (among other places).  Note that some primitives are only
 *  implemented as part of the API and have no "internal" helper.
 *  (This is the case when an internal helper would not really be
 *  useful; e.g. the operation is rare, uses value stack heavily,
 *  etc.)
 *
 *  The operation arguments depend on what is required to implement
 *  the operation:
 *
 *    - If an operation is simple and stateless, and has no side
 *      effects, it won't take an duk_hthread argument and its
 *      arguments may be duk_tval pointers (which are safe as long
 *      as no side effects take place).
 *
 *    - If complex coercions are required (e.g. a "ToNumber" coercion)
 *      or errors may be thrown, the operation takes an duk_hthread
 *      argument.  This also implies that the operation may have
 *      arbitrary side effects, invalidating any duk_tval pointers.
 *
 *    - For operations with potential side effects, arguments can be
 *      taken in several ways:
 *
 *      a) as duk_tval pointers, which makes sense if the "common case"
 *         can be resolved without side effects (e.g. coercion); the
 *         arguments are pushed to the valstack for coercion if
 *         necessary
 *
 *      b) as duk_tval values
 *
 *      c) implicitly on value stack top
 *
 *      d) as indices to the value stack
 *
 *  Future work:
 *
 *     - Argument styles may not be the most sensible in every case now.
 *
 *     - In-place coercions might be useful for several operations, if
 *       in-place coercion is OK for the bytecode executor and the API.
 */

#include "duk_internal.h"

/*
 *  [[DefaultValue]]  (E5 Section 8.12.8)
 *
 *  ==> implemented in the API.
 */

/*
 *  ToPrimitive()  (E5 Section 9.1)
 *
 *  ==> implemented in the API.
 */

/*
 *  ToBoolean()  (E5 Section 9.2)
 */

DUK_INTERNAL duk_bool_t duk_js_toboolean(duk_tval *tv) {
        switch (DUK_TVAL_GET_TAG(tv)) {
        case DUK_TAG_UNDEFINED:
        case DUK_TAG_NULL:
                return 0;
        case DUK_TAG_BOOLEAN:
                return DUK_TVAL_GET_BOOLEAN(tv);
        case DUK_TAG_STRING: {
                duk_hstring *h = DUK_TVAL_GET_STRING(tv);
                DUK_ASSERT(h != NULL);
                return (DUK_HSTRING_GET_BYTELEN(h) > 0 ? 1 : 0);
        }
        case DUK_TAG_OBJECT: {
                return 1;
        }
        case DUK_TAG_BUFFER: {
                /* mimic semantics for strings */
                duk_hbuffer *h = DUK_TVAL_GET_BUFFER(tv);
                DUK_ASSERT(h != NULL);
                return (DUK_HBUFFER_GET_SIZE(h) > 0 ? 1 : 0);
        }
        case DUK_TAG_POINTER: {
                void *p = DUK_TVAL_GET_POINTER(tv);
                return (p != NULL ? 1 : 0);
        }
        case DUK_TAG_LIGHTFUNC: {
                return 1;
        }
#if defined(DUK_USE_FASTINT)
        case DUK_TAG_FASTINT:
                if (DUK_TVAL_GET_FASTINT(tv) != 0) {
                        return 1;
                } else {
                        return 0;
                }
#endif
        default: {
                /* number */
                duk_double_t d;
                int c;
                DUK_ASSERT(!DUK_TVAL_IS_UNUSED(tv));
                DUK_ASSERT(DUK_TVAL_IS_DOUBLE(tv));
                d = DUK_TVAL_GET_DOUBLE(tv);
                c = DUK_FPCLASSIFY((double) d);
                if (c == DUK_FP_ZERO || c == DUK_FP_NAN) {
                        return 0;
                } else {
                        return 1;
                }
        }
        }
        DUK_UNREACHABLE();
}

/*
 *  ToNumber()  (E5 Section 9.3)
 *
 *  Value to convert must be on stack top, and is popped before exit.
 *
 *  See: http://www.cs.indiana.edu/~burger/FP-Printing-PLDI96.pdf
 *       http://www.cs.indiana.edu/~burger/fp/index.html
 *
 *  Notes on the conversion:
 *
 *    - There are specific requirements on the accuracy of the conversion
 *      through a "Mathematical Value" (MV), so this conversion is not
 *      trivial.
 *
 *    - Quick rejects (e.g. based on first char) are difficult because
 *      the grammar allows leading and trailing white space.
 *
 *    - Quick reject based on string length is difficult even after
 *      accounting for white space; there may be arbitrarily many
 *      decimal digits.
 *
 *    - Standard grammar allows decimal values ("123"), hex values
 *      ("0x123") and infinities
 *
 *    - Unlike source code literals, ToNumber() coerces empty strings
 *      and strings with only whitespace to zero (not NaN).
 */

/* E5 Section 9.3.1 */
DUK_LOCAL duk_double_t duk__tonumber_string_raw(duk_hthread *thr) {
        duk_context *ctx = (duk_context *) thr;
        duk_small_uint_t s2n_flags;
        duk_double_t d;

        /* Quite lenient, e.g. allow empty as zero, but don't allow trailing
         * garbage.
         */
        s2n_flags = DUK_S2N_FLAG_TRIM_WHITE |
                    DUK_S2N_FLAG_ALLOW_EXP |
                    DUK_S2N_FLAG_ALLOW_PLUS |
                    DUK_S2N_FLAG_ALLOW_MINUS |
                    DUK_S2N_FLAG_ALLOW_INF |
                    DUK_S2N_FLAG_ALLOW_FRAC |
                    DUK_S2N_FLAG_ALLOW_NAKED_FRAC |
                    DUK_S2N_FLAG_ALLOW_EMPTY_FRAC |
                    DUK_S2N_FLAG_ALLOW_EMPTY_AS_ZERO |
                    DUK_S2N_FLAG_ALLOW_LEADING_ZERO |
                    DUK_S2N_FLAG_ALLOW_AUTO_HEX_INT;

        duk_numconv_parse(ctx, 10 /*radix*/, s2n_flags);
        d = duk_get_number(ctx, -1);
        duk_pop(ctx);

        return d;
}

DUK_INTERNAL duk_double_t duk_js_tonumber(duk_hthread *thr, duk_tval *tv) {
        duk_context *ctx = (duk_hthread *) thr;

        DUK_ASSERT(thr != NULL);
        DUK_ASSERT(tv != NULL);

        switch (DUK_TVAL_GET_TAG(tv)) {
        case DUK_TAG_UNDEFINED: {
                /* return a specific NaN (although not strictly necessary) */
                duk_double_union du;
                DUK_DBLUNION_SET_NAN(&du);
                DUK_ASSERT(DUK_DBLUNION_IS_NORMALIZED(&du));
                return du.d;
        }
        case DUK_TAG_NULL: {
                /* +0.0 */
                return 0.0;
        }
        case DUK_TAG_BOOLEAN: {
                if (DUK_TVAL_IS_BOOLEAN_TRUE(tv)) {
                        return 1.0;
                }
                return 0.0;
        }
        case DUK_TAG_STRING: {
                duk_hstring *h = DUK_TVAL_GET_STRING(tv);
                duk_push_hstring(ctx, h);
                return duk__tonumber_string_raw(thr);
        }
        case DUK_TAG_OBJECT: {
                /* Note: ToPrimitive(object,hint) == [[DefaultValue]](object,hint),
                 * so use [[DefaultValue]] directly.
                 */
                duk_double_t d;
                duk_push_tval(ctx, tv);
                duk_to_defaultvalue(ctx, -1, DUK_HINT_NUMBER);  /* 'tv' becomes invalid */

                /* recursive call for a primitive value (guaranteed not to cause second
                 * recursion).
                 */
                d = duk_js_tonumber(thr, duk_require_tval(ctx, -1));

                duk_pop(ctx);
                return d;
        }
        case DUK_TAG_BUFFER: {
                /* Coerce like a string.  This makes sense because addition also treats
                 * buffers like strings.
                 */
                duk_hbuffer *h = DUK_TVAL_GET_BUFFER(tv);
                duk_push_hbuffer(ctx, h);
                duk_to_string(ctx, -1);  /* XXX: expensive, but numconv now expects to see a string */
                return duk__tonumber_string_raw(thr);
        }
        case DUK_TAG_POINTER: {
                /* Coerce like boolean */
                void *p = DUK_TVAL_GET_POINTER(tv);
                return (p != NULL ? 1.0 : 0.0);
        }
        case DUK_TAG_LIGHTFUNC: {
                /* +(function(){}) -> NaN */
                return DUK_DOUBLE_NAN;
        }
#if defined(DUK_USE_FASTINT)
        case DUK_TAG_FASTINT:
                return (duk_double_t) DUK_TVAL_GET_FASTINT(tv);
#endif
        default: {
                /* number */
                DUK_ASSERT(!DUK_TVAL_IS_UNUSED(tv));
                DUK_ASSERT(DUK_TVAL_IS_DOUBLE(tv));
                return DUK_TVAL_GET_DOUBLE(tv);
        }
        }

        DUK_UNREACHABLE();
}

/*
 *  ToInteger()  (E5 Section 9.4)
 */

/* exposed, used by e.g. duk_bi_date.c */
DUK_INTERNAL duk_double_t duk_js_tointeger_number(duk_double_t x) {
        duk_small_int_t c = (duk_small_int_t) DUK_FPCLASSIFY(x);

        if (c == DUK_FP_NAN) {
                return 0.0;
        } else if (c == DUK_FP_ZERO || c == DUK_FP_INFINITE) {
                /* XXX: FP_ZERO check can be removed, the else clause handles it
                 * correctly (preserving sign).
                 */
                return x;
        } else {
                duk_small_int_t s = (duk_small_int_t) DUK_SIGNBIT(x);
                x = DUK_FLOOR(DUK_FABS(x));  /* truncate towards zero */
                if (s) {
                        x = -x;
                }
                return x;
        }
}

DUK_INTERNAL duk_double_t duk_js_tointeger(duk_hthread *thr, duk_tval *tv) {
        /* XXX: fastint */
        duk_double_t d = duk_js_tonumber(thr, tv);  /* invalidates tv */
        return duk_js_tointeger_number(d);
}

/*
 *  ToInt32(), ToUint32(), ToUint16()  (E5 Sections 9.5, 9.6, 9.7)
 */

/* combined algorithm matching E5 Sections 9.5 and 9.6 */
DUK_LOCAL duk_double_t duk__toint32_touint32_helper(duk_double_t x, duk_bool_t is_toint32) {
        duk_small_int_t c = (duk_small_int_t) DUK_FPCLASSIFY(x);
        duk_small_int_t s;

        if (c == DUK_FP_NAN || c == DUK_FP_ZERO || c == DUK_FP_INFINITE) {
                return 0.0;
        }


        /* x = sign(x) * floor(abs(x)), i.e. truncate towards zero, keep sign */
        s = (duk_small_int_t) DUK_SIGNBIT(x);
        x = DUK_FLOOR(DUK_FABS(x));
        if (s) {
                x = -x;
        }

        /* NOTE: fmod(x) result sign is same as sign of x, which
         * differs from what Javascript wants (see Section 9.6).
         */

        x = DUK_FMOD(x, DUK_DOUBLE_2TO32);    /* -> x in ]-2**32, 2**32[ */

        if (x < 0.0) {
                x += DUK_DOUBLE_2TO32;
        }
        /* -> x in [0, 2**32[ */

        if (is_toint32) {
                if (x >= DUK_DOUBLE_2TO31) {
                        /* x in [2**31, 2**32[ */

                        x -= DUK_DOUBLE_2TO32;  /* -> x in [-2**31,2**31[ */
                }
        }

        return x;
}

DUK_INTERNAL duk_int32_t duk_js_toint32(duk_hthread *thr, duk_tval *tv) {
        duk_double_t d;

#if defined(DUK_USE_FASTINT)
        if (DUK_TVAL_IS_FASTINT(tv)) {
                return DUK_TVAL_GET_FASTINT_I32(tv);
        }
#endif

        d = duk_js_tonumber(thr, tv);  /* invalidates tv */
        d = duk__toint32_touint32_helper(d, 1);
        DUK_ASSERT(DUK_FPCLASSIFY(d) == DUK_FP_ZERO || DUK_FPCLASSIFY(d) == DUK_FP_NORMAL);
        DUK_ASSERT(d >= -2147483648.0 && d <= 2147483647.0);  /* [-0x80000000,0x7fffffff] */
        DUK_ASSERT(d == ((duk_double_t) ((duk_int32_t) d)));  /* whole, won't clip */
        return (duk_int32_t) d;
}


DUK_INTERNAL duk_uint32_t duk_js_touint32(duk_hthread *thr, duk_tval *tv) {
        duk_double_t d;

#if defined(DUK_USE_FASTINT)
        if (DUK_TVAL_IS_FASTINT(tv)) {
                return DUK_TVAL_GET_FASTINT_U32(tv);
        }
#endif

        d = duk_js_tonumber(thr, tv);  /* invalidates tv */
        d = duk__toint32_touint32_helper(d, 0);
        DUK_ASSERT(DUK_FPCLASSIFY(d) == DUK_FP_ZERO || DUK_FPCLASSIFY(d) == DUK_FP_NORMAL);
        DUK_ASSERT(d >= 0.0 && d <= 4294967295.0);  /* [0x00000000, 0xffffffff] */
        DUK_ASSERT(d == ((duk_double_t) ((duk_uint32_t) d)));  /* whole, won't clip */
        return (duk_uint32_t) d;

}

DUK_INTERNAL duk_uint16_t duk_js_touint16(duk_hthread *thr, duk_tval *tv) {
        /* should be a safe way to compute this */
        return (duk_uint16_t) (duk_js_touint32(thr, tv) & 0x0000ffffU);
}

/*
 *  ToString()  (E5 Section 9.8)
 *
 *  ==> implemented in the API.
 */

/*
 *  ToObject()  (E5 Section 9.9)
 *
 *  ==> implemented in the API.
 */

/*
 *  CheckObjectCoercible()  (E5 Section 9.10)
 *
 *  Note: no API equivalent now.
 */

#if 0  /* unused */
DUK_INTERNAL void duk_js_checkobjectcoercible(duk_hthread *thr, duk_tval *tv_x) {
        duk_small_uint_t tag = DUK_TVAL_GET_TAG(tv_x);

        /* Note: this must match ToObject() behavior */

        if (tag == DUK_TAG_UNDEFINED ||
            tag == DUK_TAG_NULL ||
            tag == DUK_TAG_POINTER ||
            tag == DUK_TAG_BUFFER) {
                DUK_ERROR_TYPE(thr, "not object coercible");
        }
}
#endif

/*
 *  IsCallable()  (E5 Section 9.11)
 *
 *  XXX: API equivalent is a separate implementation now, and this has
 *  currently no callers.
 */

#if 0  /* unused */
DUK_INTERNAL duk_bool_t duk_js_iscallable(duk_tval *tv_x) {
        duk_hobject *obj;

        if (!DUK_TVAL_IS_OBJECT(tv_x)) {
                return 0;
        }
        obj = DUK_TVAL_GET_OBJECT(tv_x);
        DUK_ASSERT(obj != NULL);

        return DUK_HOBJECT_IS_CALLABLE(obj);
}
#endif

/*
 *  Loose equality, strict equality, and SameValue (E5 Sections 11.9.1, 11.9.4,
 *  9.12).  These have much in common so they can share some helpers.
 *
 *  Future work notes:
 *
 *    - Current implementation (and spec definition) has recursion; this should
 *      be fixed if possible.
 *
 *    - String-to-number coercion should be possible without going through the
 *      value stack (and be more compact) if a shared helper is invoked.
 */

/* Note that this is the same operation for strict and loose equality:
 *  - E5 Section 11.9.3, step 1.c (loose)
 *  - E5 Section 11.9.6, step 4 (strict)
 */

DUK_LOCAL duk_bool_t duk__js_equals_number(duk_double_t x, duk_double_t y) {
#if defined(DUK_USE_PARANOID_MATH)
        /* Straightforward algorithm, makes fewer compiler assumptions. */
        duk_small_int_t cx = (duk_small_int_t) DUK_FPCLASSIFY(x);
        duk_small_int_t cy = (duk_small_int_t) DUK_FPCLASSIFY(y);
        if (cx == DUK_FP_NAN || cy == DUK_FP_NAN) {
                return 0;
        }
        if (cx == DUK_FP_ZERO && cy == DUK_FP_ZERO) {
                return 1;
        }
        if (x == y) {
                return 1;
        }
        return 0;
#else  /* DUK_USE_PARANOID_MATH */
        /* Better equivalent algorithm.  If the compiler is compliant, C and
         * Ecmascript semantics are identical for this particular comparison.
         * In particular, NaNs must never compare equal and zeroes must compare
         * equal regardless of sign.  Could also use a macro, but this inlines
         * already nicely (no difference on gcc, for instance).
         */
        if (x == y) {
                /* IEEE requires that NaNs compare false */
                DUK_ASSERT(DUK_FPCLASSIFY(x) != DUK_FP_NAN);
                DUK_ASSERT(DUK_FPCLASSIFY(y) != DUK_FP_NAN);
                return 1;
        } else {
                /* IEEE requires that zeros compare the same regardless
                 * of their signed, so if both x and y are zeroes, they
                 * are caught above.
                 */
                DUK_ASSERT(!(DUK_FPCLASSIFY(x) == DUK_FP_ZERO && DUK_FPCLASSIFY(y) == DUK_FP_ZERO));
                return 0;
        }
#endif  /* DUK_USE_PARANOID_MATH */
}

DUK_LOCAL duk_bool_t duk__js_samevalue_number(duk_double_t x, duk_double_t y) {
#if defined(DUK_USE_PARANOID_MATH)
        duk_small_int_t cx = (duk_small_int_t) DUK_FPCLASSIFY(x);
        duk_small_int_t cy = (duk_small_int_t) DUK_FPCLASSIFY(y);

        if (cx == DUK_FP_NAN && cy == DUK_FP_NAN) {
                /* SameValue(NaN, NaN) = true, regardless of NaN sign or extra bits */
                return 1;
        }
        if (cx == DUK_FP_ZERO && cy == DUK_FP_ZERO) {
                /* Note: cannot assume that a non-zero return value of signbit() would
                 * always be the same -- hence cannot (portably) use something like:
                 *
                 *     signbit(x) == signbit(y)
                 */
                duk_small_int_t sx = (DUK_SIGNBIT(x) ? 1 : 0);
                duk_small_int_t sy = (DUK_SIGNBIT(y) ? 1 : 0);
                return (sx == sy);
        }

        /* normal comparison; known:
         *   - both x and y are not NaNs (but one of them can be)
         *   - both x and y are not zero (but one of them can be)
         *   - x and y may be denormal or infinite
         */

        return (x == y);
#else  /* DUK_USE_PARANOID_MATH */
        duk_small_int_t cx = (duk_small_int_t) DUK_FPCLASSIFY(x);
        duk_small_int_t cy = (duk_small_int_t) DUK_FPCLASSIFY(y);

        if (x == y) {
                /* IEEE requires that NaNs compare false */
                DUK_ASSERT(DUK_FPCLASSIFY(x) != DUK_FP_NAN);
                DUK_ASSERT(DUK_FPCLASSIFY(y) != DUK_FP_NAN);

                /* Using classification has smaller footprint than direct comparison. */
                if (DUK_UNLIKELY(cx == DUK_FP_ZERO && cy == DUK_FP_ZERO)) {
                        /* Note: cannot assume that a non-zero return value of signbit() would
                         * always be the same -- hence cannot (portably) use something like:
                         *
                         *     signbit(x) == signbit(y)
                         */
                        duk_small_int_t sx = (DUK_SIGNBIT(x) ? 1 : 0);
                        duk_small_int_t sy = (DUK_SIGNBIT(y) ? 1 : 0);
                        return (sx == sy);
                }
                return 1;
        } else {
                /* IEEE requires that zeros compare the same regardless
                 * of their signed, so if both x and y are zeroes, they
                 * are caught above.
                 */
                DUK_ASSERT(!(DUK_FPCLASSIFY(x) == DUK_FP_ZERO && DUK_FPCLASSIFY(y) == DUK_FP_ZERO));

                /* Difference to non-strict/strict comparison is that NaNs compare
                 * equal and signed zero signs matter.
                 */
                if (DUK_UNLIKELY(cx == DUK_FP_NAN && cy == DUK_FP_NAN)) {
                        /* SameValue(NaN, NaN) = true, regardless of NaN sign or extra bits */
                        return 1;
                }
                return 0;
        }
#endif  /* DUK_USE_PARANOID_MATH */
}

DUK_INTERNAL duk_bool_t duk_js_equals_helper(duk_hthread *thr, duk_tval *tv_x, duk_tval *tv_y, duk_small_int_t flags) {
        duk_context *ctx = (duk_context *) thr;
        duk_tval *tv_tmp;

        /* If flags != 0 (strict or SameValue), thr can be NULL.  For loose
         * equals comparison it must be != NULL.
         */
        DUK_ASSERT(flags != 0 || thr != NULL);

        /*
         *  Same type?
         *
         *  Note: since number values have no explicit tag in the 8-byte
         *  representation, need the awkward if + switch.
         */

#if defined(DUK_USE_FASTINT)
        if (DUK_TVAL_IS_FASTINT(tv_x) && DUK_TVAL_IS_FASTINT(tv_y)) {
                if (DUK_TVAL_GET_FASTINT(tv_x) == DUK_TVAL_GET_FASTINT(tv_y)) {
                        return 1;
                } else {
                        return 0;
                }
        }
        else
#endif
        if (DUK_TVAL_IS_NUMBER(tv_x) && DUK_TVAL_IS_NUMBER(tv_y)) {
                /* Catches both doubles and cases where only one argument is a fastint */
                if (DUK_UNLIKELY((flags & DUK_EQUALS_FLAG_SAMEVALUE) != 0)) {
                        /* SameValue */
                        return duk__js_samevalue_number(DUK_TVAL_GET_NUMBER(tv_x),
                                                        DUK_TVAL_GET_NUMBER(tv_y));
                } else {
                        /* equals and strict equals */
                        return duk__js_equals_number(DUK_TVAL_GET_NUMBER(tv_x),
                                                     DUK_TVAL_GET_NUMBER(tv_y));
                }
        } else if (DUK_TVAL_GET_TAG(tv_x) == DUK_TVAL_GET_TAG(tv_y)) {
                switch (DUK_TVAL_GET_TAG(tv_x)) {
                case DUK_TAG_UNDEFINED:
                case DUK_TAG_NULL: {
                        return 1;
                }
                case DUK_TAG_BOOLEAN: {
                        return DUK_TVAL_GET_BOOLEAN(tv_x) == DUK_TVAL_GET_BOOLEAN(tv_y);
                }
                case DUK_TAG_POINTER: {
                        return DUK_TVAL_GET_POINTER(tv_x) == DUK_TVAL_GET_POINTER(tv_y);
                }
                case DUK_TAG_STRING:
                case DUK_TAG_OBJECT: {
                        /* heap pointer comparison suffices */
                        return DUK_TVAL_GET_HEAPHDR(tv_x) == DUK_TVAL_GET_HEAPHDR(tv_y);
                }
                case DUK_TAG_BUFFER: {
                        if ((flags & (DUK_EQUALS_FLAG_STRICT | DUK_EQUALS_FLAG_SAMEVALUE)) != 0) {
                                /* heap pointer comparison suffices */
                                return DUK_TVAL_GET_HEAPHDR(tv_x) == DUK_TVAL_GET_HEAPHDR(tv_y);
                        } else {
                                /* non-strict equality for buffers compares contents */
                                duk_hbuffer *h_x = DUK_TVAL_GET_BUFFER(tv_x);
                                duk_hbuffer *h_y = DUK_TVAL_GET_BUFFER(tv_y);
                                duk_size_t len_x = DUK_HBUFFER_GET_SIZE(h_x);
                                duk_size_t len_y = DUK_HBUFFER_GET_SIZE(h_y);
                                void *buf_x;
                                void *buf_y;
                                if (len_x != len_y) {
                                        return 0;
                                }
                                buf_x = (void *) DUK_HBUFFER_GET_DATA_PTR(thr->heap, h_x);
                                buf_y = (void *) DUK_HBUFFER_GET_DATA_PTR(thr->heap, h_y);
                                /* if len_x == len_y == 0, buf_x and/or buf_y may
                                 * be NULL, but that's OK.
                                 */
                                DUK_ASSERT(len_x == len_y);
                                DUK_ASSERT(len_x == 0 || buf_x != NULL);
                                DUK_ASSERT(len_y == 0 || buf_y != NULL);
                                return (DUK_MEMCMP((const void *) buf_x, (const void *) buf_y, (size_t) len_x) == 0) ? 1 : 0;
                        }
                }
                case DUK_TAG_LIGHTFUNC: {
                        /* At least 'magic' has a significant impact on function
                         * identity.
                         */
                        duk_small_uint_t lf_flags_x;
                        duk_small_uint_t lf_flags_y;
                        duk_c_function func_x;
                        duk_c_function func_y;

                        DUK_TVAL_GET_LIGHTFUNC(tv_x, func_x, lf_flags_x);
                        DUK_TVAL_GET_LIGHTFUNC(tv_y, func_y, lf_flags_y);
                        return ((func_x == func_y) && (lf_flags_x == lf_flags_y)) ? 1 : 0;
                }
#if defined(DUK_USE_FASTINT)
                case DUK_TAG_FASTINT:
#endif
                default: {
                        DUK_ASSERT(!DUK_TVAL_IS_UNUSED(tv_x));
                        DUK_ASSERT(!DUK_TVAL_IS_UNUSED(tv_y));
                        DUK_ASSERT(DUK_TVAL_IS_NUMBER(tv_x));
                        DUK_ASSERT(DUK_TVAL_IS_NUMBER(tv_y));
                        DUK_UNREACHABLE();
                        return 0;
                }
                }
        }

        if ((flags & (DUK_EQUALS_FLAG_STRICT | DUK_EQUALS_FLAG_SAMEVALUE)) != 0) {
                return 0;
        }

        DUK_ASSERT(flags == 0);  /* non-strict equality from here on */

        /*
         *  Types are different; various cases for non-strict comparison
         *
         *  Since comparison is symmetric, we use a "swap trick" to reduce
         *  code size.
         */

        /* Undefined/null are considered equal (e.g. "null == undefined" -> true). */
        if ((DUK_TVAL_IS_UNDEFINED(tv_x) && DUK_TVAL_IS_NULL(tv_y)) ||
            (DUK_TVAL_IS_NULL(tv_x) && DUK_TVAL_IS_UNDEFINED(tv_y))) {
                return 1;
        }

        /* Number/string-or-buffer -> coerce string to number (e.g. "'1.5' == 1.5" -> true). */
        if (DUK_TVAL_IS_NUMBER(tv_x) && (DUK_TVAL_IS_STRING(tv_y) || DUK_TVAL_IS_BUFFER(tv_y))) {
                /* the next 'if' is guaranteed to match after swap */
                tv_tmp = tv_x;
                tv_x = tv_y;
                tv_y = tv_tmp;
        }
        if ((DUK_TVAL_IS_STRING(tv_x) || DUK_TVAL_IS_BUFFER(tv_x)) && DUK_TVAL_IS_NUMBER(tv_y)) {
                /* XXX: this is possible without resorting to the value stack */
                duk_double_t d1, d2;
                d2 = DUK_TVAL_GET_NUMBER(tv_y);
                duk_push_tval(ctx, tv_x);
                duk_to_string(ctx, -1);  /* buffer values are coerced first to string here */
                duk_to_number(ctx, -1);
                d1 = duk_require_number(ctx, -1);
                duk_pop(ctx);
                return duk__js_equals_number(d1, d2);
        }

        /* Buffer/string -> compare contents. */
        if (DUK_TVAL_IS_BUFFER(tv_x) && DUK_TVAL_IS_STRING(tv_y)) {
                tv_tmp = tv_x;
                tv_x = tv_y;
                tv_y = tv_tmp;
        }
        if (DUK_TVAL_IS_STRING(tv_x) && DUK_TVAL_IS_BUFFER(tv_y)) {
                duk_hstring *h_x = DUK_TVAL_GET_STRING(tv_x);
                duk_hbuffer *h_y = DUK_TVAL_GET_BUFFER(tv_y);
                duk_size_t len_x = DUK_HSTRING_GET_BYTELEN(h_x);
                duk_size_t len_y = DUK_HBUFFER_GET_SIZE(h_y);
                const void *buf_x;
                const void *buf_y;
                if (len_x != len_y) {
                        return 0;
                }
                buf_x = (const void *) DUK_HSTRING_GET_DATA(h_x);
                buf_y = (const void *) DUK_HBUFFER_GET_DATA_PTR(thr->heap, h_y);
                /* if len_x == len_y == 0, buf_x and/or buf_y may
                 * be NULL, but that's OK.
                 */
                DUK_ASSERT(len_x == len_y);
                DUK_ASSERT(len_x == 0 || buf_x != NULL);
                DUK_ASSERT(len_y == 0 || buf_y != NULL);
                return (DUK_MEMCMP((const void *) buf_x, (const void *) buf_y, (size_t) len_x) == 0) ? 1 : 0;
        }

        /* Boolean/any -> coerce boolean to number and try again.  If boolean is
         * compared to a pointer, the final comparison after coercion now always
         * yields false (as pointer vs. number compares to false), but this is
         * not special cased.
         */
        if (DUK_TVAL_IS_BOOLEAN(tv_x)) {
                tv_tmp = tv_x;
                tv_x = tv_y;
                tv_y = tv_tmp;
        }
        if (DUK_TVAL_IS_BOOLEAN(tv_y)) {
                /* ToNumber(bool) is +1.0 or 0.0.  Tagged boolean value is always 0 or 1. */
                duk_bool_t rc;
                DUK_ASSERT(DUK_TVAL_GET_BOOLEAN(tv_y) == 0 || DUK_TVAL_GET_BOOLEAN(tv_y) == 1);
                duk_push_tval(ctx, tv_x);
                duk_push_int(ctx, DUK_TVAL_GET_BOOLEAN(tv_y));
                rc = duk_js_equals_helper(thr,
                                          DUK_GET_TVAL_NEGIDX(ctx, -2),
                                          DUK_GET_TVAL_NEGIDX(ctx, -1),
                                          0 /*flags:nonstrict*/);
                duk_pop_2(ctx);
                return rc;
        }

        /* String-number-buffer/object -> coerce object to primitive (apparently without hint), then try again. */
        if ((DUK_TVAL_IS_STRING(tv_x) || DUK_TVAL_IS_NUMBER(tv_x) || DUK_TVAL_IS_BUFFER(tv_x)) &&
            DUK_TVAL_IS_OBJECT(tv_y)) {
                tv_tmp = tv_x;
                tv_x = tv_y;
                tv_y = tv_tmp;
        }
        if (DUK_TVAL_IS_OBJECT(tv_x) &&
            (DUK_TVAL_IS_STRING(tv_y) || DUK_TVAL_IS_NUMBER(tv_y) || DUK_TVAL_IS_BUFFER(tv_y))) {
                duk_bool_t rc;
                duk_push_tval(ctx, tv_x);
                duk_push_tval(ctx, tv_y);
                duk_to_primitive(ctx, -2, DUK_HINT_NONE);  /* apparently no hint? */
                rc = duk_js_equals_helper(thr,
                                          DUK_GET_TVAL_NEGIDX(ctx, -2),
                                          DUK_GET_TVAL_NEGIDX(ctx, -1),
                                          0 /*flags:nonstrict*/);
                duk_pop_2(ctx);
                return rc;
        }

        /* Nothing worked -> not equal. */
        return 0;
}

/*
 *  Comparisons (x >= y, x > y, x <= y, x < y)
 *
 *  E5 Section 11.8.5: implement 'x < y' and then use negate and eval_left_first
 *  flags to get the rest.
 */

/* XXX: this should probably just operate on the stack top, because it
 * needs to push stuff on the stack anyway...
 */

DUK_INTERNAL duk_small_int_t duk_js_data_compare(const duk_uint8_t *buf1, const duk_uint8_t *buf2, duk_size_t len1, duk_size_t len2) {
        duk_size_t prefix_len;
        duk_small_int_t rc;

        prefix_len = (len1 <= len2 ? len1 : len2);

        /* DUK_MEMCMP() is guaranteed to return zero (equal) for zero length
         * inputs so no zero length check is needed.
         */
        rc = DUK_MEMCMP((const void *) buf1,
                        (const void *) buf2,
                        (size_t) prefix_len);

        if (rc < 0) {
                return -1;
        } else if (rc > 0) {
                return 1;
        }

        /* prefix matches, lengths matter now */
        if (len1 < len2) {
                /* e.g. "x" < "xx" */
                return -1;
        } else if (len1 > len2) {
                return 1;
        }

        return 0;
}

DUK_INTERNAL duk_small_int_t duk_js_string_compare(duk_hstring *h1, duk_hstring *h2) {
        /*
         *  String comparison (E5 Section 11.8.5, step 4), which
         *  needs to compare codepoint by codepoint.
         *
         *  However, UTF-8 allows us to use strcmp directly: the shared
         *  prefix will be encoded identically (UTF-8 has unique encoding)
         *  and the first differing character can be compared with a simple
         *  unsigned byte comparison (which strcmp does).
         *
         *  This will not work properly for non-xutf-8 strings, but this
         *  is not an issue for compliance.
         */

        DUK_ASSERT(h1 != NULL);
        DUK_ASSERT(h2 != NULL);

        return duk_js_data_compare((const duk_uint8_t *) DUK_HSTRING_GET_DATA(h1),
                                   (const duk_uint8_t *) DUK_HSTRING_GET_DATA(h2),
                                   (duk_size_t) DUK_HSTRING_GET_BYTELEN(h1),
                                   (duk_size_t) DUK_HSTRING_GET_BYTELEN(h2));
}

#if 0  /* unused */
DUK_INTERNAL duk_small_int_t duk_js_buffer_compare(duk_heap *heap, duk_hbuffer *h1, duk_hbuffer *h2) {
        /* Similar to String comparison. */

        DUK_ASSERT(h1 != NULL);
        DUK_ASSERT(h2 != NULL);
        DUK_UNREF(heap);

        return duk_js_data_compare((const duk_uint8_t *) DUK_HBUFFER_GET_DATA_PTR(heap, h1),
                                   (const duk_uint8_t *) DUK_HBUFFER_GET_DATA_PTR(heap, h2),
                                   (duk_size_t) DUK_HBUFFER_GET_SIZE(h1),
                                   (duk_size_t) DUK_HBUFFER_GET_SIZE(h2));
}
#endif

DUK_INTERNAL duk_bool_t duk_js_compare_helper(duk_hthread *thr, duk_tval *tv_x, duk_tval *tv_y, duk_small_int_t flags) {
        duk_context *ctx = (duk_context *) thr;
        duk_double_t d1, d2;
        duk_small_int_t c1, c2;
        duk_small_int_t s1, s2;
        duk_small_int_t rc;
        duk_bool_t retval;

        /* Fast path for fastints */
#if defined(DUK_USE_FASTINT)
        if (DUK_TVAL_IS_FASTINT(tv_x) && DUK_TVAL_IS_FASTINT(tv_y)) {
                duk_int64_t v1 = DUK_TVAL_GET_FASTINT(tv_x);
                duk_int64_t v2 = DUK_TVAL_GET_FASTINT(tv_y);
                if (v1 < v2) {
                        /* 'lt is true' */
                        retval = 1;
                } else {
                        retval = 0;
                }
                if (flags & DUK_COMPARE_FLAG_NEGATE) {
                        retval ^= 1;
                }
                return retval;
        }
#endif  /* DUK_USE_FASTINT */

        /* Fast path for numbers (one of which may be a fastint) */
#if 1  /* XXX: make fast paths optional for size minimization? */
        if (DUK_TVAL_IS_NUMBER(tv_x) && DUK_TVAL_IS_NUMBER(tv_y)) {
                d1 = DUK_TVAL_GET_NUMBER(tv_x);
                d2 = DUK_TVAL_GET_NUMBER(tv_y);
                c1 = DUK_FPCLASSIFY(d1);
                c2 = DUK_FPCLASSIFY(d2);

                if (c1 == DUK_FP_NORMAL && c2 == DUK_FP_NORMAL) {
                        /* XXX: this is a very narrow check, and doesn't cover
                         * zeroes, subnormals, infinities, which compare normally.
                         */

                        if (d1 < d2) {
                                /* 'lt is true' */
                                retval = 1;
                        } else {
                                retval = 0;
                        }
                        if (flags & DUK_COMPARE_FLAG_NEGATE) {
                                retval ^= 1;
                        }
                        return retval;
                }
        }
#endif

        /* Slow path */

        duk_push_tval(ctx, tv_x);
        duk_push_tval(ctx, tv_y);

        if (flags & DUK_COMPARE_FLAG_EVAL_LEFT_FIRST) {
                duk_to_primitive(ctx, -2, DUK_HINT_NUMBER);
                duk_to_primitive(ctx, -1, DUK_HINT_NUMBER);
        } else {
                duk_to_primitive(ctx, -1, DUK_HINT_NUMBER);
                duk_to_primitive(ctx, -2, DUK_HINT_NUMBER);
        }

        /* Note: reuse variables */
        tv_x = DUK_GET_TVAL_NEGIDX(ctx, -2);
        tv_y = DUK_GET_TVAL_NEGIDX(ctx, -1);

        if (DUK_TVAL_IS_STRING(tv_x) && DUK_TVAL_IS_STRING(tv_y)) {
                duk_hstring *h1 = DUK_TVAL_GET_STRING(tv_x);
                duk_hstring *h2 = DUK_TVAL_GET_STRING(tv_y);
                DUK_ASSERT(h1 != NULL);
                DUK_ASSERT(h2 != NULL);

                rc = duk_js_string_compare(h1, h2);
                if (rc < 0) {
                        goto lt_true;
                } else {
                        goto lt_false;
                }
        } else {
                /* Ordering should not matter (E5 Section 11.8.5, step 3.a) but
                 * preserve it just in case.
                 */

                if (flags & DUK_COMPARE_FLAG_EVAL_LEFT_FIRST) {
                        d1 = duk_to_number(ctx, -2);
                        d2 = duk_to_number(ctx, -1);
                } else {
                        d2 = duk_to_number(ctx, -1);
                        d1 = duk_to_number(ctx, -2);
                }

                c1 = (duk_small_int_t) DUK_FPCLASSIFY(d1);
                s1 = (duk_small_int_t) DUK_SIGNBIT(d1);
                c2 = (duk_small_int_t) DUK_FPCLASSIFY(d2);
                s2 = (duk_small_int_t) DUK_SIGNBIT(d2);

                if (c1 == DUK_FP_NAN || c2 == DUK_FP_NAN) {
                        goto lt_undefined;
                }

                if (c1 == DUK_FP_ZERO && c2 == DUK_FP_ZERO) {
                        /* For all combinations: +0 < +0, +0 < -0, -0 < +0, -0 < -0,
                         * steps e, f, and g.
                         */
                        goto lt_false;
                }

                if (d1 == d2) {
                        goto lt_false;
                }

                if (c1 == DUK_FP_INFINITE && s1 == 0) {
                        /* x == +Infinity */
                        goto lt_false;
                }

                if (c2 == DUK_FP_INFINITE && s2 == 0) {
                        /* y == +Infinity */
                        goto lt_true;
                }

                if (c2 == DUK_FP_INFINITE && s2 != 0) {
                        /* y == -Infinity */
                        goto lt_false;
                }

                if (c1 == DUK_FP_INFINITE && s1 != 0) {
                        /* x == -Infinity */
                        goto lt_true;
                }

                if (d1 < d2) {
                        goto lt_true;
                }

                goto lt_false;
        }

 lt_undefined:
        /* Note: undefined from Section 11.8.5 always results in false
         * return (see e.g. Section 11.8.3) - hence special treatment here.
         */
        retval = 0;
        goto cleanup;

 lt_true:
        if (flags & DUK_COMPARE_FLAG_NEGATE) {
                retval = 0;
                goto cleanup;
        } else {
                retval = 1;
                goto cleanup;
        }
        /* never here */

 lt_false:
        if (flags & DUK_COMPARE_FLAG_NEGATE) {
                retval = 1;
                goto cleanup;
        } else {
                retval = 0;
                goto cleanup;
        }
        /* never here */

 cleanup:
        duk_pop_2(ctx);
        return retval;
}

/*
 *  instanceof
 */

/*
 *  E5 Section 11.8.6 describes the main algorithm, which uses
 *  [[HasInstance]].  [[HasInstance]] is defined for only
 *  function objects:
 *
 *    - Normal functions:
 *      E5 Section 15.3.5.3
 *    - Functions established with Function.prototype.bind():
 *      E5 Section 15.3.4.5.3
 *
 *  For other objects, a TypeError is thrown.
 *
 *  Limited Proxy support: don't support 'getPrototypeOf' trap but
 *  continue lookup in Proxy target if the value is a Proxy.
 */

DUK_INTERNAL duk_bool_t duk_js_instanceof(duk_hthread *thr, duk_tval *tv_x, duk_tval *tv_y) {
        duk_context *ctx = (duk_context *) thr;
        duk_hobject *func;
        duk_hobject *val;
        duk_hobject *proto;
        duk_uint_t sanity;

        /*
         *  Get the values onto the stack first.  It would be possible to cover
         *  some normal cases without resorting to the value stack.
         *
         *  The right hand side could be a light function (as they generally
         *  behave like objects).  Light functions never have a 'prototype'
         *  property so E5.1 Section 15.3.5.3 step 3 always throws a TypeError.
         *  Using duk_require_hobject() is thus correct (except for error msg).
         */

        duk_push_tval(ctx, tv_x);
        duk_push_tval(ctx, tv_y);
        func = duk_require_hobject(ctx, -1);

        /*
         *  For bound objects, [[HasInstance]] just calls the target function
         *  [[HasInstance]].  If that is again a bound object, repeat until
         *  we find a non-bound Function object.
         */

        /* XXX: this bound function resolution also happens elsewhere,
         * move into a shared helper.
         */

        sanity = DUK_HOBJECT_BOUND_CHAIN_SANITY;
        do {
                /* check func supports [[HasInstance]] (this is checked for every function
                 * in the bound chain, including the final one)
                 */

                if (!DUK_HOBJECT_IS_CALLABLE(func)) {
                        /*
                         *  Note: of native Ecmascript objects, only Function instances
                         *  have a [[HasInstance]] internal property.  Custom objects might
                         *  also have it, but not in current implementation.
                         *
                         *  XXX: add a separate flag, DUK_HOBJECT_FLAG_ALLOW_INSTANCEOF?
                         */
                        DUK_ERROR_TYPE(thr, "invalid instanceof rval");
                }

                if (!DUK_HOBJECT_HAS_BOUND(func)) {
                        break;
                }

                /* [ ... lval rval ] */

                duk_get_prop_stridx(ctx, -1, DUK_STRIDX_INT_TARGET);         /* -> [ ... lval rval new_rval ] */
                duk_replace(ctx, -1);                                        /* -> [ ... lval new_rval ] */
                func = duk_require_hobject(ctx, -1);

                /* func support for [[HasInstance]] checked in the beginning of the loop */
        } while (--sanity > 0);

        if (sanity == 0) {
                DUK_ERROR_RANGE(thr, DUK_STR_BOUND_CHAIN_LIMIT);
        }

        /*
         *  'func' is now a non-bound object which supports [[HasInstance]]
         *  (which here just means DUK_HOBJECT_FLAG_CALLABLE).  Move on
         *  to execute E5 Section 15.3.5.3.
         */

        DUK_ASSERT(!DUK_HOBJECT_HAS_BOUND(func));
        DUK_ASSERT(DUK_HOBJECT_IS_CALLABLE(func));

        /* [ ... lval rval(func) ] */

        /* Handle lightfuncs through object coercion for now. */
        /* XXX: direct implementation */
        val = duk_get_hobject_or_lfunc_coerce(ctx, -2);
        if (!val) {
                goto pop_and_false;
        }

        duk_get_prop_stridx(ctx, -1, DUK_STRIDX_PROTOTYPE);  /* -> [ ... lval rval rval.prototype ] */
        proto = duk_require_hobject(ctx, -1);
        duk_pop(ctx);  /* -> [ ... lval rval ] */

        DUK_ASSERT(val != NULL);

#if defined(DUK_USE_ES6_PROXY)
        val = duk_hobject_resolve_proxy_target(thr, val);
        DUK_ASSERT(val != NULL);
#endif

        sanity = DUK_HOBJECT_PROTOTYPE_CHAIN_SANITY;
        do {
                /*
                 *  Note: prototype chain is followed BEFORE first comparison.  This
                 *  means that the instanceof lval is never itself compared to the
                 *  rval.prototype property.  This is apparently intentional, see E5
                 *  Section 15.3.5.3, step 4.a.
                 *
                 *  Also note:
                 *
                 *      js> (function() {}) instanceof Function
                 *      true
                 *      js> Function instanceof Function
                 *      true
                 *
                 *  For the latter, h_proto will be Function.prototype, which is the
                 *  built-in Function prototype.  Because Function.[[Prototype]] is
                 *  also the built-in Function prototype, the result is true.
                 */

                DUK_ASSERT(val != NULL);
                val = DUK_HOBJECT_GET_PROTOTYPE(thr->heap, val);

                if (!val) {
                        goto pop_and_false;
                }

                DUK_ASSERT(val != NULL);
#if defined(DUK_USE_ES6_PROXY)
                val = duk_hobject_resolve_proxy_target(thr, val);
#endif

                if (val == proto) {
                        goto pop_and_true;
                }

                /* follow prototype chain */
        } while (--sanity > 0);

        if (sanity == 0) {
                DUK_ERROR_RANGE(thr, DUK_STR_PROTOTYPE_CHAIN_LIMIT);
        }
        DUK_UNREACHABLE();

 pop_and_false:
        duk_pop_2(ctx);
        return 0;

 pop_and_true:
        duk_pop_2(ctx);
        return 1;
}

/*
 *  in
 */

/*
 *  E5 Sections 11.8.7, 8.12.6.
 *
 *  Basically just a property existence check using [[HasProperty]].
 */

DUK_INTERNAL duk_bool_t duk_js_in(duk_hthread *thr, duk_tval *tv_x, duk_tval *tv_y) {
        duk_context *ctx = (duk_context *) thr;
        duk_bool_t retval;

        /*
         *  Get the values onto the stack first.  It would be possible to cover
         *  some normal cases without resorting to the value stack (e.g. if
         *  lval is already a string).
         */

        /* XXX: The ES5/5.1/6 specifications require that the key in 'key in obj'
         * must be string coerced before the internal HasProperty() algorithm is
         * invoked.  A fast path skipping coercion could be safely implemented for
         * numbers (as number-to-string coercion has no side effects).  For ES6
         * proxy behavior, the trap 'key' argument must be in a string coerced
         * form (which is a shame).
         */

        /* TypeError if rval is not an object (or lightfunc which should behave
         * like a Function instance).
         */
        duk_push_tval(ctx, tv_x);
        duk_push_tval(ctx, tv_y);
        duk_require_type_mask(ctx, -1, DUK_TYPE_MASK_OBJECT | DUK_TYPE_MASK_LIGHTFUNC);
        duk_to_string(ctx, -2);               /* coerce lval with ToString() */

        retval = duk_hobject_hasprop(thr,
                                     DUK_GET_TVAL_NEGIDX(ctx, -1),
                                     DUK_GET_TVAL_NEGIDX(ctx, -2));

        duk_pop_2(ctx);
        return retval;
}

/*
 *  typeof
 *
 *  E5 Section 11.4.3.
 *
 *  Very straightforward.  The only question is what to return for our
 *  non-standard tag / object types.
 *
 *  There is an unfortunate string constant define naming problem with
 *  typeof return values for e.g. "Object" and "object"; careful with
 *  the built-in string defines.  The LC_XXX defines are used for the
 *  lowercase variants now.
 */

DUK_INTERNAL duk_hstring *duk_js_typeof(duk_hthread *thr, duk_tval *tv_x) {
        duk_small_int_t stridx = 0;

        DUK_UNREF(thr);

        switch (DUK_TVAL_GET_TAG(tv_x)) {
        case DUK_TAG_UNDEFINED: {
                stridx = DUK_STRIDX_LC_UNDEFINED;
                break;
        }
        case DUK_TAG_NULL: {
                /* Note: not a typo, "object" is returned for a null value */
                stridx = DUK_STRIDX_LC_OBJECT;
                break;
        }
        case DUK_TAG_BOOLEAN: {
                stridx = DUK_STRIDX_LC_BOOLEAN;
                break;
        }
        case DUK_TAG_POINTER: {
                /* implementation specific */
                stridx = DUK_STRIDX_LC_POINTER;
                break;
        }
        case DUK_TAG_STRING: {
                stridx = DUK_STRIDX_LC_STRING;
                break;
        }
        case DUK_TAG_OBJECT: {
                duk_hobject *obj = DUK_TVAL_GET_OBJECT(tv_x);
                DUK_ASSERT(obj != NULL);
                if (DUK_HOBJECT_IS_CALLABLE(obj)) {
                        stridx = DUK_STRIDX_LC_FUNCTION;
                } else {
                        stridx = DUK_STRIDX_LC_OBJECT;
                }
                break;
        }
        case DUK_TAG_BUFFER: {
                /* implementation specific */
                stridx = DUK_STRIDX_LC_BUFFER;
                break;
        }
        case DUK_TAG_LIGHTFUNC: {
                stridx = DUK_STRIDX_LC_FUNCTION;
                break;
        }
#if defined(DUK_USE_FASTINT)
        case DUK_TAG_FASTINT:
#endif
        default: {
                /* number */
                DUK_ASSERT(!DUK_TVAL_IS_UNUSED(tv_x));
                DUK_ASSERT(DUK_TVAL_IS_NUMBER(tv_x));
                stridx = DUK_STRIDX_LC_NUMBER;
                break;
        }
        }

        DUK_ASSERT(stridx >= 0 && stridx < DUK_HEAP_NUM_STRINGS);
        return DUK_HTHREAD_GET_STRING(thr, stridx);
}

/*
 *  Array index and length
 *
 *  Array index: E5 Section 15.4
 *  Array length: E5 Section 15.4.5.1 steps 3.c - 3.d (array length write)
 *
 *  The DUK_HSTRING_GET_ARRIDX_SLOW() and DUK_HSTRING_GET_ARRIDX_FAST() macros
 *  call duk_js_to_arrayindex_string_helper().
 */

DUK_INTERNAL duk_small_int_t duk_js_to_arrayindex_raw_string(const duk_uint8_t *str, duk_uint32_t blen, duk_uarridx_t *out_idx) {
        duk_uarridx_t res;

        if (blen == 0 || blen > 10) {
                goto parse_fail;
        }
        if (str[0] == DUK_ASC_0 && blen > 1) {
                goto parse_fail;
        }

        /* Accept 32-bit decimal integers, no leading zeroes, signs, etc.
         * Leading zeroes are not accepted (zero index "0" is an exception
         * handled above).
         */

        res = 0;
        while (blen-- > 0) {
                duk_uint8_t c = *str++;
                if (c >= DUK_ASC_0 && c <= DUK_ASC_9) {
                        /* Careful overflow handling.  When multiplying by 10:
                         * - 0x19999998 x 10 = 0xfffffff0: no overflow, and adding
                         *   0...9 is safe.
                         * - 0x19999999 x 10 = 0xfffffffa: no overflow, adding
                         *   0...5 is safe, 6...9 overflows.
                         * - 0x1999999a x 10 = 0x100000004: always overflow.
                         */
                        if (DUK_UNLIKELY(res >= 0x19999999UL)) {
                                if (res >= 0x1999999aUL) {
                                        /* Always overflow. */
                                        goto parse_fail;
                                }
                                DUK_ASSERT(res == 0x19999999UL);
                                c -= DUK_ASC_0;
                                if (c >= 6) {
                                        goto parse_fail;
                                }
                                res = 0xfffffffaUL + c;
                                DUK_ASSERT(res >= 0xfffffffaUL);
                                DUK_ASSERT_DISABLE(res <= 0xffffffffUL);  /* range */
                        } else {
                                res = res * 10U + (duk_uint32_t) (c - DUK_ASC_0);
                        }
                } else {
                        goto parse_fail;
                }
        }

        *out_idx = res;
        return 1;

 parse_fail:
        *out_idx = DUK_HSTRING_NO_ARRAY_INDEX;
        return 0;
}

/* Called by duk_hstring.h macros */
DUK_INTERNAL duk_uarridx_t duk_js_to_arrayindex_string_helper(duk_hstring *h) {
        duk_uarridx_t res;
        duk_small_int_t rc;

        if (!DUK_HSTRING_HAS_ARRIDX(h)) {
                return DUK_HSTRING_NO_ARRAY_INDEX;
        }

        rc = duk_js_to_arrayindex_raw_string(DUK_HSTRING_GET_DATA(h),
                                             DUK_HSTRING_GET_BYTELEN(h),
                                             &res);
        DUK_UNREF(rc);
        DUK_ASSERT(rc != 0);
        return res;
}