ceph/src/civetweb/src/third_party/duktape-1.3.0/src-separate/duk_util_hashprime.c

   1 /*
   2  *  Round a number upwards to a prime (not usually the nearest one).
   3  *
   4  *  Uses a table of successive 32-bit primes whose ratio is roughly
   5  *  constant.  This keeps the relative upwards 'rounding error' bounded
   6  *  and the data size small.  A simple 'predict-correct' compression is
   7  *  used to compress primes to one byte per prime.  See genhashsizes.py
   8  *  for details.
   9  *
  10  *  The minimum prime returned here must be coordinated with the possible
  11  *  probe sequence steps in duk_hobject and duk_heap stringtable.
  12  */
  13
  14 #include "duk_internal.h"
  15
  16 /* Awkward inclusion condition: drop out of compilation if not needed by any
  17  * call site: object hash part or probing stringtable.
  18  */
  19 #if defined(DUK_USE_HOBJECT_HASH_PART) || defined(DUK_USE_STRTAB_PROBE)
  20
  21 /* hash size ratio goal, must match genhashsizes.py */
  22 #define DUK__HASH_SIZE_RATIO   1177  /* floor(1.15 * (1 << 10)) */
  23
  24 /* prediction corrections for prime list (see genhashsizes.py) */
  25 DUK_LOCAL const duk_int8_t duk__hash_size_corrections[] = {
  26         17,  /* minimum prime */
  27         4, 3, 4, 1, 4, 1, 1, 2, 2, 2, 2, 1, 6, 6, 9, 5, 1, 2, 2, 5, 1, 3, 3, 3,
  28         5, 4, 4, 2, 4, 8, 3, 4, 23, 2, 4, 7, 8, 11, 2, 12, 15, 10, 1, 1, 5, 1, 5,
  29         8, 9, 17, 14, 10, 7, 5, 2, 46, 21, 1, 9, 9, 4, 4, 10, 23, 36, 6, 20, 29,
  30         18, 6, 19, 21, 16, 11, 5, 5, 48, 9, 1, 39, 14, 8, 4, 29, 9, 1, 15, 48, 12,
  31         22, 6, 15, 27, 4, 2, 17, 28, 8, 9, 4, 5, 8, 3, 3, 8, 37, 11, 15, 8, 30,
  32         43, 6, 33, 41, 5, 20, 32, 41, 38, 24, 77, 14, 19, 11, 4, 35, 18, 19, 41,
  33         10, 23, 16, 9, 2,
  34         -1
  35 };
  36
  37 /* probe steps (see genhashsizes.py), currently assumed to be 32 entries long
  38  * (DUK_UTIL_GET_HASH_PROBE_STEP macro).
  39  */
  40 DUK_INTERNAL duk_uint8_t duk_util_probe_steps[32] = {
  41         2, 3, 5, 7, 11, 13, 19, 31, 41, 47, 59, 67, 73, 79, 89, 101, 103, 107,
  42         109, 127, 137, 139, 149, 157, 163, 167, 173, 181, 191, 193, 197, 199
  43 };
  44
  45 DUK_INTERNAL duk_uint32_t duk_util_get_hash_prime(duk_uint32_t size) {
  46         const duk_int8_t *p = duk__hash_size_corrections;
  47         duk_uint32_t curr;
  48
  49         curr = (duk_uint32_t) *p++;
  50         for (;;) {
  51                 duk_small_int_t t = (duk_small_int_t) *p++;
  52                 if (t < 0) {
  53                         /* may happen if size is very close to 2^32-1 */
  54                         break;
  55                 }
  56
  57                 /* prediction: portable variant using doubles if 64-bit values not available */
  58 #ifdef DUK_USE_64BIT_OPS
  59                 curr = (duk_uint32_t) ((((duk_uint64_t) curr) * ((duk_uint64_t) DUK__HASH_SIZE_RATIO)) >> 10);
  60 #else
  61                 /* 32-bit x 11-bit = 43-bit, fits accurately into a double */
  62                 curr = (duk_uint32_t) DUK_FLOOR(((double) curr) * ((double) DUK__HASH_SIZE_RATIO) / 1024.0);
  63 #endif
  64
  65                 /* correction */
  66                 curr += t;
  67
  68                 DUK_DDD(DUK_DDDPRINT("size=%ld, curr=%ld", (long) size, (long) curr));
  69
  70                 if (curr >= size) {
  71                         return curr;
  72                 }
  73         }
  74         return 0;
  75 }
  76
  77 #endif  /* DUK_USE_HOBJECT_HASH_PART || DUK_USE_STRTAB_PROBE */