src/tools/clippy/clippy_lints/src/floating_point_arithmetic.rs

   1 use clippy_utils::consts::{
   2     constant, constant_simple, Constant,
   3     Constant::{Int, F32, F64},
   4 };
   5 use clippy_utils::diagnostics::span_lint_and_sugg;
   6 use clippy_utils::higher;
   7 use clippy_utils::{eq_expr_value, get_parent_expr, in_constant, numeric_literal, peel_blocks, sugg};
   8 use if_chain::if_chain;
   9 use rustc_errors::Applicability;
  10 use rustc_hir::{BinOpKind, Expr, ExprKind, PathSegment, UnOp};
  11 use rustc_lint::{LateContext, LateLintPass};
  12 use rustc_middle::ty;
  13 use rustc_session::{declare_lint_pass, declare_tool_lint};
  14 use rustc_span::source_map::Spanned;
  15
  16 use rustc_ast::ast;
  17 use std::f32::consts as f32_consts;
  18 use std::f64::consts as f64_consts;
  19 use sugg::Sugg;
  20
  21 declare_clippy_lint! {
  22     /// ### What it does
  23     /// Looks for floating-point expressions that
  24     /// can be expressed using built-in methods to improve accuracy
  25     /// at the cost of performance.
  26     ///
  27     /// ### Why is this bad?
  28     /// Negatively impacts accuracy.
  29     ///
  30     /// ### Example
  31     /// ```rust
  32     /// let a = 3f32;
  33     /// let _ = a.powf(1.0 / 3.0);
  34     /// let _ = (1.0 + a).ln();
  35     /// let _ = a.exp() - 1.0;
  36     /// ```
  37     ///
  38     /// Use instead:
  39     /// ```rust
  40     /// let a = 3f32;
  41     /// let _ = a.cbrt();
  42     /// let _ = a.ln_1p();
  43     /// let _ = a.exp_m1();
  44     /// ```
  45     #[clippy::version = "1.43.0"]
  46     pub IMPRECISE_FLOPS,
  47     nursery,
  48     "usage of imprecise floating point operations"
  49 }
  50
  51 declare_clippy_lint! {
  52     /// ### What it does
  53     /// Looks for floating-point expressions that
  54     /// can be expressed using built-in methods to improve both
  55     /// accuracy and performance.
  56     ///
  57     /// ### Why is this bad?
  58     /// Negatively impacts accuracy and performance.
  59     ///
  60     /// ### Example
  61     /// ```rust
  62     /// use std::f32::consts::E;
  63     ///
  64     /// let a = 3f32;
  65     /// let _ = (2f32).powf(a);
  66     /// let _ = E.powf(a);
  67     /// let _ = a.powf(1.0 / 2.0);
  68     /// let _ = a.log(2.0);
  69     /// let _ = a.log(10.0);
  70     /// let _ = a.log(E);
  71     /// let _ = a.powf(2.0);
  72     /// let _ = a * 2.0 + 4.0;
  73     /// let _ = if a < 0.0 {
  74     ///     -a
  75     /// } else {
  76     ///     a
  77     /// };
  78     /// let _ = if a < 0.0 {
  79     ///     a
  80     /// } else {
  81     ///     -a
  82     /// };
  83     /// ```
  84     ///
  85     /// is better expressed as
  86     ///
  87     /// ```rust
  88     /// use std::f32::consts::E;
  89     ///
  90     /// let a = 3f32;
  91     /// let _ = a.exp2();
  92     /// let _ = a.exp();
  93     /// let _ = a.sqrt();
  94     /// let _ = a.log2();
  95     /// let _ = a.log10();
  96     /// let _ = a.ln();
  97     /// let _ = a.powi(2);
  98     /// let _ = a.mul_add(2.0, 4.0);
  99     /// let _ = a.abs();
 100     /// let _ = -a.abs();
 101     /// ```
 102     #[clippy::version = "1.43.0"]
 103     pub SUBOPTIMAL_FLOPS,
 104     nursery,
 105     "usage of sub-optimal floating point operations"
 106 }
 107
 108 declare_lint_pass!(FloatingPointArithmetic => [
 109     IMPRECISE_FLOPS,
 110     SUBOPTIMAL_FLOPS
 111 ]);
 112
 113 // Returns the specialized log method for a given base if base is constant
 114 // and is one of 2, 10 and e
 115 fn get_specialized_log_method(cx: &LateContext<'_>, base: &Expr<'_>) -> Option<&'static str> {
 116     if let Some((value, _)) = constant(cx, cx.typeck_results(), base) {
 117         if F32(2.0) == value || F64(2.0) == value {
 118             return Some("log2");
 119         } else if F32(10.0) == value || F64(10.0) == value {
 120             return Some("log10");
 121         } else if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
 122             return Some("ln");
 123         }
 124     }
 125
 126     None
 127 }
 128
 129 // Adds type suffixes and parenthesis to method receivers if necessary
 130 fn prepare_receiver_sugg<'a>(cx: &LateContext<'_>, mut expr: &'a Expr<'a>) -> Sugg<'a> {
 131     let mut suggestion = Sugg::hir(cx, expr, "..");
 132
 133     if let ExprKind::Unary(UnOp::Neg, inner_expr) = &expr.kind {
 134         expr = inner_expr;
 135     }
 136
 137     if_chain! {
 138         // if the expression is a float literal and it is unsuffixed then
 139         // add a suffix so the suggestion is valid and unambiguous
 140         if let ty::Float(float_ty) = cx.typeck_results().expr_ty(expr).kind();
 141         if let ExprKind::Lit(lit) = &expr.kind;
 142         if let ast::LitKind::Float(sym, ast::LitFloatType::Unsuffixed) = lit.node;
 143         then {
 144             let op = format!(
 145                 "{}{}{}",
 146                 suggestion,
 147                 // Check for float literals without numbers following the decimal
 148                 // separator such as `2.` and adds a trailing zero
 149                 if sym.as_str().ends_with('.') {
 150                     "0"
 151                 } else {
 152                     ""
 153                 },
 154                 float_ty.name_str()
 155             ).into();
 156
 157             suggestion = match suggestion {
 158                 Sugg::MaybeParen(_) => Sugg::MaybeParen(op),
 159                 _ => Sugg::NonParen(op)
 160             };
 161         }
 162     }
 163
 164     suggestion.maybe_par()
 165 }
 166
 167 fn check_log_base(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args: &[Expr<'_>]) {
 168     if let Some(method) = get_specialized_log_method(cx, &args[0]) {
 169         span_lint_and_sugg(
 170             cx,
 171             SUBOPTIMAL_FLOPS,
 172             expr.span,
 173             "logarithm for bases 2, 10 and e can be computed more accurately",
 174             "consider using",
 175             format!("{}.{}()", Sugg::hir(cx, receiver, "..").maybe_par(), method),
 176             Applicability::MachineApplicable,
 177         );
 178     }
 179 }
 180
 181 // TODO: Lint expressions of the form `(x + y).ln()` where y > 1 and
 182 // suggest usage of `(x + (y - 1)).ln_1p()` instead
 183 fn check_ln1p(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>) {
 184     if let ExprKind::Binary(
 185         Spanned {
 186             node: BinOpKind::Add, ..
 187         },
 188         lhs,
 189         rhs,
 190     ) = receiver.kind
 191     {
 192         let recv = match (
 193             constant(cx, cx.typeck_results(), lhs),
 194             constant(cx, cx.typeck_results(), rhs),
 195         ) {
 196             (Some((value, _)), _) if F32(1.0) == value || F64(1.0) == value => rhs,
 197             (_, Some((value, _))) if F32(1.0) == value || F64(1.0) == value => lhs,
 198             _ => return,
 199         };
 200
 201         span_lint_and_sugg(
 202             cx,
 203             IMPRECISE_FLOPS,
 204             expr.span,
 205             "ln(1 + x) can be computed more accurately",
 206             "consider using",
 207             format!("{}.ln_1p()", prepare_receiver_sugg(cx, recv)),
 208             Applicability::MachineApplicable,
 209         );
 210     }
 211 }
 212
 213 // Returns an integer if the float constant is a whole number and it can be
 214 // converted to an integer without loss of precision. For now we only check
 215 // ranges [-16777215, 16777216) for type f32 as whole number floats outside
 216 // this range are lossy and ambiguous.
 217 #[expect(clippy::cast_possible_truncation)]
 218 fn get_integer_from_float_constant(value: &Constant) -> Option<i32> {
 219     match value {
 220         F32(num) if num.fract() == 0.0 => {
 221             if (-16_777_215.0..16_777_216.0).contains(num) {
 222                 Some(num.round() as i32)
 223             } else {
 224                 None
 225             }
 226         },
 227         F64(num) if num.fract() == 0.0 => {
 228             if (-2_147_483_648.0..2_147_483_648.0).contains(num) {
 229                 Some(num.round() as i32)
 230             } else {
 231                 None
 232             }
 233         },
 234         _ => None,
 235     }
 236 }
 237
 238 fn check_powf(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args: &[Expr<'_>]) {
 239     // Check receiver
 240     if let Some((value, _)) = constant(cx, cx.typeck_results(), receiver) {
 241         if let Some(method) = if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
 242             Some("exp")
 243         } else if F32(2.0) == value || F64(2.0) == value {
 244             Some("exp2")
 245         } else {
 246             None
 247         } {
 248             span_lint_and_sugg(
 249                 cx,
 250                 SUBOPTIMAL_FLOPS,
 251                 expr.span,
 252                 "exponent for bases 2 and e can be computed more accurately",
 253                 "consider using",
 254                 format!("{}.{}()", prepare_receiver_sugg(cx, &args[0]), method),
 255                 Applicability::MachineApplicable,
 256             );
 257         }
 258     }
 259
 260     // Check argument
 261     if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[0]) {
 262         let (lint, help, suggestion) = if F32(1.0 / 2.0) == value || F64(1.0 / 2.0) == value {
 263             (
 264                 SUBOPTIMAL_FLOPS,
 265                 "square-root of a number can be computed more efficiently and accurately",
 266                 format!("{}.sqrt()", Sugg::hir(cx, receiver, "..").maybe_par()),
 267             )
 268         } else if F32(1.0 / 3.0) == value || F64(1.0 / 3.0) == value {
 269             (
 270                 IMPRECISE_FLOPS,
 271                 "cube-root of a number can be computed more accurately",
 272                 format!("{}.cbrt()", Sugg::hir(cx, receiver, "..").maybe_par()),
 273             )
 274         } else if let Some(exponent) = get_integer_from_float_constant(&value) {
 275             (
 276                 SUBOPTIMAL_FLOPS,
 277                 "exponentiation with integer powers can be computed more efficiently",
 278                 format!(
 279                     "{}.powi({})",
 280                     Sugg::hir(cx, receiver, "..").maybe_par(),
 281                     numeric_literal::format(&exponent.to_string(), None, false)
 282                 ),
 283             )
 284         } else {
 285             return;
 286         };
 287
 288         span_lint_and_sugg(
 289             cx,
 290             lint,
 291             expr.span,
 292             help,
 293             "consider using",
 294             suggestion,
 295             Applicability::MachineApplicable,
 296         );
 297     }
 298 }
 299
 300 fn check_powi(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args: &[Expr<'_>]) {
 301     if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[0]) {
 302         if value == Int(2) {
 303             if let Some(parent) = get_parent_expr(cx, expr) {
 304                 if let Some(grandparent) = get_parent_expr(cx, parent) {
 305                     if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, receiver, ..) = grandparent.kind
 306                     {
 307                         if method_name.as_str() == "sqrt" && detect_hypot(cx, receiver).is_some() {
 308                             return;
 309                         }
 310                     }
 311                 }
 312
 313                 if let ExprKind::Binary(
 314                     Spanned {
 315                         node: BinOpKind::Add, ..
 316                     },
 317                     lhs,
 318                     rhs,
 319                 ) = parent.kind
 320                 {
 321                     let other_addend = if lhs.hir_id == expr.hir_id { rhs } else { lhs };
 322
 323                     span_lint_and_sugg(
 324                         cx,
 325                         SUBOPTIMAL_FLOPS,
 326                         parent.span,
 327                         "multiply and add expressions can be calculated more efficiently and accurately",
 328                         "consider using",
 329                         format!(
 330                             "{}.mul_add({}, {})",
 331                             Sugg::hir(cx, receiver, "..").maybe_par(),
 332                             Sugg::hir(cx, receiver, ".."),
 333                             Sugg::hir(cx, other_addend, ".."),
 334                         ),
 335                         Applicability::MachineApplicable,
 336                     );
 337                 }
 338             }
 339         }
 340     }
 341 }
 342
 343 fn detect_hypot(cx: &LateContext<'_>, receiver: &Expr<'_>) -> Option<String> {
 344     if let ExprKind::Binary(
 345         Spanned {
 346             node: BinOpKind::Add, ..
 347         },
 348         add_lhs,
 349         add_rhs,
 350     ) = receiver.kind
 351     {
 352         // check if expression of the form x * x + y * y
 353         if_chain! {
 354             if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, lmul_lhs, lmul_rhs) = add_lhs.kind;
 355             if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, rmul_lhs, rmul_rhs) = add_rhs.kind;
 356             if eq_expr_value(cx, lmul_lhs, lmul_rhs);
 357             if eq_expr_value(cx, rmul_lhs, rmul_rhs);
 358             then {
 359                 return Some(format!("{}.hypot({})", Sugg::hir(cx, lmul_lhs, "..").maybe_par(), Sugg::hir(cx, rmul_lhs, "..")));
 360             }
 361         }
 362
 363         // check if expression of the form x.powi(2) + y.powi(2)
 364         if_chain! {
 365             if let ExprKind::MethodCall(
 366                 PathSegment { ident: lmethod_name, .. },
 367                 largs_0, [largs_1, ..],
 368                 _
 369             ) = &add_lhs.kind;
 370             if let ExprKind::MethodCall(
 371                 PathSegment { ident: rmethod_name, .. },
 372                 rargs_0, [rargs_1, ..],
 373                 _
 374             ) = &add_rhs.kind;
 375             if lmethod_name.as_str() == "powi" && rmethod_name.as_str() == "powi";
 376             if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), largs_1);
 377             if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), rargs_1);
 378             if Int(2) == lvalue && Int(2) == rvalue;
 379             then {
 380                 return Some(format!("{}.hypot({})", Sugg::hir(cx, largs_0, "..").maybe_par(), Sugg::hir(cx, rargs_0, "..")));
 381             }
 382         }
 383     }
 384
 385     None
 386 }
 387
 388 fn check_hypot(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>) {
 389     if let Some(message) = detect_hypot(cx, receiver) {
 390         span_lint_and_sugg(
 391             cx,
 392             IMPRECISE_FLOPS,
 393             expr.span,
 394             "hypotenuse can be computed more accurately",
 395             "consider using",
 396             message,
 397             Applicability::MachineApplicable,
 398         );
 399     }
 400 }
 401
 402 // TODO: Lint expressions of the form `x.exp() - y` where y > 1
 403 // and suggest usage of `x.exp_m1() - (y - 1)` instead
 404 fn check_expm1(cx: &LateContext<'_>, expr: &Expr<'_>) {
 405     if_chain! {
 406         if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, lhs, rhs) = expr.kind;
 407         if cx.typeck_results().expr_ty(lhs).is_floating_point();
 408         if let Some((value, _)) = constant(cx, cx.typeck_results(), rhs);
 409         if F32(1.0) == value || F64(1.0) == value;
 410         if let ExprKind::MethodCall(path, self_arg, ..) = &lhs.kind;
 411         if cx.typeck_results().expr_ty(self_arg).is_floating_point();
 412         if path.ident.name.as_str() == "exp";
 413         then {
 414             span_lint_and_sugg(
 415                 cx,
 416                 IMPRECISE_FLOPS,
 417                 expr.span,
 418                 "(e.pow(x) - 1) can be computed more accurately",
 419                 "consider using",
 420                 format!(
 421                     "{}.exp_m1()",
 422                     Sugg::hir(cx, self_arg, "..").maybe_par()
 423                 ),
 424                 Applicability::MachineApplicable,
 425             );
 426         }
 427     }
 428 }
 429
 430 fn is_float_mul_expr<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
 431     if_chain! {
 432         if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, lhs, rhs) = &expr.kind;
 433         if cx.typeck_results().expr_ty(lhs).is_floating_point();
 434         if cx.typeck_results().expr_ty(rhs).is_floating_point();
 435         then {
 436             return Some((lhs, rhs));
 437         }
 438     }
 439
 440     None
 441 }
 442
 443 // TODO: Fix rust-lang/rust-clippy#4735
 444 fn check_mul_add(cx: &LateContext<'_>, expr: &Expr<'_>) {
 445     if let ExprKind::Binary(
 446         Spanned {
 447             node: BinOpKind::Add, ..
 448         },
 449         lhs,
 450         rhs,
 451     ) = &expr.kind
 452     {
 453         if let Some(parent) = get_parent_expr(cx, expr) {
 454             if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, receiver, ..) = parent.kind {
 455                 if method_name.as_str() == "sqrt" && detect_hypot(cx, receiver).is_some() {
 456                     return;
 457                 }
 458             }
 459         }
 460
 461         let (recv, arg1, arg2) = if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, lhs) {
 462             (inner_lhs, inner_rhs, rhs)
 463         } else if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, rhs) {
 464             (inner_lhs, inner_rhs, lhs)
 465         } else {
 466             return;
 467         };
 468
 469         span_lint_and_sugg(
 470             cx,
 471             SUBOPTIMAL_FLOPS,
 472             expr.span,
 473             "multiply and add expressions can be calculated more efficiently and accurately",
 474             "consider using",
 475             format!(
 476                 "{}.mul_add({}, {})",
 477                 prepare_receiver_sugg(cx, recv),
 478                 Sugg::hir(cx, arg1, ".."),
 479                 Sugg::hir(cx, arg2, ".."),
 480             ),
 481             Applicability::MachineApplicable,
 482         );
 483     }
 484 }
 485
 486 /// Returns true iff expr is an expression which tests whether or not
 487 /// test is positive or an expression which tests whether or not test
 488 /// is nonnegative.
 489 /// Used for check-custom-abs function below
 490 fn is_testing_positive(cx: &LateContext<'_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
 491     if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
 492         match op {
 493             BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, right) && eq_expr_value(cx, left, test),
 494             BinOpKind::Lt | BinOpKind::Le => is_zero(cx, left) && eq_expr_value(cx, right, test),
 495             _ => false,
 496         }
 497     } else {
 498         false
 499     }
 500 }
 501
 502 /// See [`is_testing_positive`]
 503 fn is_testing_negative(cx: &LateContext<'_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
 504     if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
 505         match op {
 506             BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, left) && eq_expr_value(cx, right, test),
 507             BinOpKind::Lt | BinOpKind::Le => is_zero(cx, right) && eq_expr_value(cx, left, test),
 508             _ => false,
 509         }
 510     } else {
 511         false
 512     }
 513 }
 514
 515 /// Returns true iff expr is some zero literal
 516 fn is_zero(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 517     match constant_simple(cx, cx.typeck_results(), expr) {
 518         Some(Constant::Int(i)) => i == 0,
 519         Some(Constant::F32(f)) => f == 0.0,
 520         Some(Constant::F64(f)) => f == 0.0,
 521         _ => false,
 522     }
 523 }
 524
 525 /// If the two expressions are negations of each other, then it returns
 526 /// a tuple, in which the first element is true iff expr1 is the
 527 /// positive expressions, and the second element is the positive
 528 /// one of the two expressions
 529 /// If the two expressions are not negations of each other, then it
 530 /// returns None.
 531 fn are_negated<'a>(cx: &LateContext<'_>, expr1: &'a Expr<'a>, expr2: &'a Expr<'a>) -> Option<(bool, &'a Expr<'a>)> {
 532     if let ExprKind::Unary(UnOp::Neg, expr1_negated) = &expr1.kind {
 533         if eq_expr_value(cx, expr1_negated, expr2) {
 534             return Some((false, expr2));
 535         }
 536     }
 537     if let ExprKind::Unary(UnOp::Neg, expr2_negated) = &expr2.kind {
 538         if eq_expr_value(cx, expr1, expr2_negated) {
 539             return Some((true, expr1));
 540         }
 541     }
 542     None
 543 }
 544
 545 fn check_custom_abs(cx: &LateContext<'_>, expr: &Expr<'_>) {
 546     if_chain! {
 547         if let Some(higher::If { cond, then, r#else: Some(r#else) }) = higher::If::hir(expr);
 548         let if_body_expr = peel_blocks(then);
 549         let else_body_expr = peel_blocks(r#else);
 550         if let Some((if_expr_positive, body)) = are_negated(cx, if_body_expr, else_body_expr);
 551         then {
 552             let positive_abs_sugg = (
 553                 "manual implementation of `abs` method",
 554                 format!("{}.abs()", Sugg::hir(cx, body, "..").maybe_par()),
 555             );
 556             let negative_abs_sugg = (
 557                 "manual implementation of negation of `abs` method",
 558                 format!("-{}.abs()", Sugg::hir(cx, body, "..").maybe_par()),
 559             );
 560             let sugg = if is_testing_positive(cx, cond, body) {
 561                 if if_expr_positive {
 562                     positive_abs_sugg
 563                 } else {
 564                     negative_abs_sugg
 565                 }
 566             } else if is_testing_negative(cx, cond, body) {
 567                 if if_expr_positive {
 568                     negative_abs_sugg
 569                 } else {
 570                     positive_abs_sugg
 571                 }
 572             } else {
 573                 return;
 574             };
 575             span_lint_and_sugg(
 576                 cx,
 577                 SUBOPTIMAL_FLOPS,
 578                 expr.span,
 579                 sugg.0,
 580                 "try",
 581                 sugg.1,
 582                 Applicability::MachineApplicable,
 583             );
 584         }
 585     }
 586 }
 587
 588 fn are_same_base_logs(cx: &LateContext<'_>, expr_a: &Expr<'_>, expr_b: &Expr<'_>) -> bool {
 589     if_chain! {
 590         if let ExprKind::MethodCall(PathSegment { ident: method_name_a, .. }, _, args_a, _) = expr_a.kind;
 591         if let ExprKind::MethodCall(PathSegment { ident: method_name_b, .. }, _, args_b, _) = expr_b.kind;
 592         then {
 593             return method_name_a.as_str() == method_name_b.as_str() &&
 594                 args_a.len() == args_b.len() &&
 595                 (
 596                     ["ln", "log2", "log10"].contains(&method_name_a.as_str()) ||
 597                     method_name_a.as_str() == "log" && args_a.len() == 1 && eq_expr_value(cx, &args_a[0], &args_b[0])
 598                 );
 599         }
 600     }
 601
 602     false
 603 }
 604
 605 fn check_log_division(cx: &LateContext<'_>, expr: &Expr<'_>) {
 606     // check if expression of the form x.logN() / y.logN()
 607     if_chain! {
 608         if let ExprKind::Binary(
 609             Spanned {
 610                 node: BinOpKind::Div, ..
 611             },
 612             lhs,
 613             rhs,
 614         ) = &expr.kind;
 615         if are_same_base_logs(cx, lhs, rhs);
 616         if let ExprKind::MethodCall(_, largs_self, ..) = &lhs.kind;
 617         if let ExprKind::MethodCall(_, rargs_self, ..) = &rhs.kind;
 618         then {
 619             span_lint_and_sugg(
 620                 cx,
 621                 SUBOPTIMAL_FLOPS,
 622                 expr.span,
 623                 "log base can be expressed more clearly",
 624                 "consider using",
 625                 format!("{}.log({})", Sugg::hir(cx, largs_self, "..").maybe_par(), Sugg::hir(cx, rargs_self, ".."),),
 626                 Applicability::MachineApplicable,
 627             );
 628         }
 629     }
 630 }
 631
 632 fn check_radians(cx: &LateContext<'_>, expr: &Expr<'_>) {
 633     if_chain! {
 634         if let ExprKind::Binary(
 635             Spanned {
 636                 node: BinOpKind::Div, ..
 637             },
 638             div_lhs,
 639             div_rhs,
 640         ) = &expr.kind;
 641         if let ExprKind::Binary(
 642             Spanned {
 643                 node: BinOpKind::Mul, ..
 644             },
 645             mul_lhs,
 646             mul_rhs,
 647         ) = &div_lhs.kind;
 648         if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), div_rhs);
 649         if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), mul_rhs);
 650         then {
 651             // TODO: also check for constant values near PI/180 or 180/PI
 652             if (F32(f32_consts::PI) == rvalue || F64(f64_consts::PI) == rvalue) &&
 653                (F32(180_f32) == lvalue || F64(180_f64) == lvalue)
 654             {
 655                 let mut proposal = format!("{}.to_degrees()", Sugg::hir(cx, mul_lhs, "..").maybe_par());
 656                 if_chain! {
 657                     if let ExprKind::Lit(ref literal) = mul_lhs.kind;
 658                     if let ast::LitKind::Float(ref value, float_type) = literal.node;
 659                     if float_type == ast::LitFloatType::Unsuffixed;
 660                     then {
 661                         if value.as_str().ends_with('.') {
 662                             proposal = format!("{}0_f64.to_degrees()", Sugg::hir(cx, mul_lhs, ".."));
 663                         } else {
 664                             proposal = format!("{}_f64.to_degrees()", Sugg::hir(cx, mul_lhs, ".."));
 665                         }
 666                     }
 667                 }
 668                 span_lint_and_sugg(
 669                     cx,
 670                     SUBOPTIMAL_FLOPS,
 671                     expr.span,
 672                     "conversion to degrees can be done more accurately",
 673                     "consider using",
 674                     proposal,
 675                     Applicability::MachineApplicable,
 676                 );
 677             } else if
 678                 (F32(180_f32) == rvalue || F64(180_f64) == rvalue) &&
 679                 (F32(f32_consts::PI) == lvalue || F64(f64_consts::PI) == lvalue)
 680             {
 681                 let mut proposal = format!("{}.to_radians()", Sugg::hir(cx, mul_lhs, "..").maybe_par());
 682                 if_chain! {
 683                     if let ExprKind::Lit(ref literal) = mul_lhs.kind;
 684                     if let ast::LitKind::Float(ref value, float_type) = literal.node;
 685                     if float_type == ast::LitFloatType::Unsuffixed;
 686                     then {
 687                         if value.as_str().ends_with('.') {
 688                             proposal = format!("{}0_f64.to_radians()", Sugg::hir(cx, mul_lhs, ".."));
 689                         } else {
 690                             proposal = format!("{}_f64.to_radians()", Sugg::hir(cx, mul_lhs, ".."));
 691                         }
 692                     }
 693                 }
 694                 span_lint_and_sugg(
 695                     cx,
 696                     SUBOPTIMAL_FLOPS,
 697                     expr.span,
 698                     "conversion to radians can be done more accurately",
 699                     "consider using",
 700                     proposal,
 701                     Applicability::MachineApplicable,
 702                 );
 703             }
 704         }
 705     }
 706 }
 707
 708 impl<'tcx> LateLintPass<'tcx> for FloatingPointArithmetic {
 709     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 710         // All of these operations are currently not const.
 711         if in_constant(cx, expr.hir_id) {
 712             return;
 713         }
 714
 715         if let ExprKind::MethodCall(path, receiver, args, _) = &expr.kind {
 716             let recv_ty = cx.typeck_results().expr_ty(receiver);
 717
 718             if recv_ty.is_floating_point() {
 719                 match path.ident.name.as_str() {
 720                     "ln" => check_ln1p(cx, expr, receiver),
 721                     "log" => check_log_base(cx, expr, receiver, args),
 722                     "powf" => check_powf(cx, expr, receiver, args),
 723                     "powi" => check_powi(cx, expr, receiver, args),
 724                     "sqrt" => check_hypot(cx, expr, receiver),
 725                     _ => {},
 726                 }
 727             }
 728         } else {
 729             check_expm1(cx, expr);
 730             check_mul_add(cx, expr);
 731             check_custom_abs(cx, expr);
 732             check_log_division(cx, expr);
 733             check_radians(cx, expr);
 734         }
 735     }
 736 }