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                 "{suggestion}{}{}",
 146                 // Check for float literals without numbers following the decimal
 147                 // separator such as `2.` and adds a trailing zero
 148                 if sym.as_str().ends_with('.') {
 149                     "0"
 150                 } else {
 151                     ""
 152                 },
 153                 float_ty.name_str()
 154             ).into();
 155
 156             suggestion = match suggestion {
 157                 Sugg::MaybeParen(_) => Sugg::MaybeParen(op),
 158                 _ => Sugg::NonParen(op)
 159             };
 160         }
 161     }
 162
 163     suggestion.maybe_par()
 164 }
 165
 166 fn check_log_base(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args: &[Expr<'_>]) {
 167     if let Some(method) = get_specialized_log_method(cx, &args[0]) {
 168         span_lint_and_sugg(
 169             cx,
 170             SUBOPTIMAL_FLOPS,
 171             expr.span,
 172             "logarithm for bases 2, 10 and e can be computed more accurately",
 173             "consider using",
 174             format!("{}.{method}()", Sugg::hir(cx, receiver, "..").maybe_par()),
 175             Applicability::MachineApplicable,
 176         );
 177     }
 178 }
 179
 180 // TODO: Lint expressions of the form `(x + y).ln()` where y > 1 and
 181 // suggest usage of `(x + (y - 1)).ln_1p()` instead
 182 fn check_ln1p(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>) {
 183     if let ExprKind::Binary(
 184         Spanned {
 185             node: BinOpKind::Add, ..
 186         },
 187         lhs,
 188         rhs,
 189     ) = receiver.kind
 190     {
 191         let recv = match (
 192             constant(cx, cx.typeck_results(), lhs),
 193             constant(cx, cx.typeck_results(), rhs),
 194         ) {
 195             (Some((value, _)), _) if F32(1.0) == value || F64(1.0) == value => rhs,
 196             (_, Some((value, _))) if F32(1.0) == value || F64(1.0) == value => lhs,
 197             _ => return,
 198         };
 199
 200         span_lint_and_sugg(
 201             cx,
 202             IMPRECISE_FLOPS,
 203             expr.span,
 204             "ln(1 + x) can be computed more accurately",
 205             "consider using",
 206             format!("{}.ln_1p()", prepare_receiver_sugg(cx, recv)),
 207             Applicability::MachineApplicable,
 208         );
 209     }
 210 }
 211
 212 // Returns an integer if the float constant is a whole number and it can be
 213 // converted to an integer without loss of precision. For now we only check
 214 // ranges [-16777215, 16777216) for type f32 as whole number floats outside
 215 // this range are lossy and ambiguous.
 216 #[expect(clippy::cast_possible_truncation)]
 217 fn get_integer_from_float_constant(value: &Constant) -> Option<i32> {
 218     match value {
 219         F32(num) if num.fract() == 0.0 => {
 220             if (-16_777_215.0..16_777_216.0).contains(num) {
 221                 Some(num.round() as i32)
 222             } else {
 223                 None
 224             }
 225         },
 226         F64(num) if num.fract() == 0.0 => {
 227             if (-2_147_483_648.0..2_147_483_648.0).contains(num) {
 228                 Some(num.round() as i32)
 229             } else {
 230                 None
 231             }
 232         },
 233         _ => None,
 234     }
 235 }
 236
 237 fn check_powf(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args: &[Expr<'_>]) {
 238     // Check receiver
 239     if let Some((value, _)) = constant(cx, cx.typeck_results(), receiver) {
 240         if let Some(method) = if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
 241             Some("exp")
 242         } else if F32(2.0) == value || F64(2.0) == value {
 243             Some("exp2")
 244         } else {
 245             None
 246         } {
 247             span_lint_and_sugg(
 248                 cx,
 249                 SUBOPTIMAL_FLOPS,
 250                 expr.span,
 251                 "exponent for bases 2 and e can be computed more accurately",
 252                 "consider using",
 253                 format!("{}.{method}()", prepare_receiver_sugg(cx, &args[0])),
 254                 Applicability::MachineApplicable,
 255             );
 256         }
 257     }
 258
 259     // Check argument
 260     if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[0]) {
 261         let (lint, help, suggestion) = if F32(1.0 / 2.0) == value || F64(1.0 / 2.0) == value {
 262             (
 263                 SUBOPTIMAL_FLOPS,
 264                 "square-root of a number can be computed more efficiently and accurately",
 265                 format!("{}.sqrt()", Sugg::hir(cx, receiver, "..").maybe_par()),
 266             )
 267         } else if F32(1.0 / 3.0) == value || F64(1.0 / 3.0) == value {
 268             (
 269                 IMPRECISE_FLOPS,
 270                 "cube-root of a number can be computed more accurately",
 271                 format!("{}.cbrt()", Sugg::hir(cx, receiver, "..").maybe_par()),
 272             )
 273         } else if let Some(exponent) = get_integer_from_float_constant(&value) {
 274             (
 275                 SUBOPTIMAL_FLOPS,
 276                 "exponentiation with integer powers can be computed more efficiently",
 277                 format!(
 278                     "{}.powi({})",
 279                     Sugg::hir(cx, receiver, "..").maybe_par(),
 280                     numeric_literal::format(&exponent.to_string(), None, false)
 281                 ),
 282             )
 283         } else {
 284             return;
 285         };
 286
 287         span_lint_and_sugg(
 288             cx,
 289             lint,
 290             expr.span,
 291             help,
 292             "consider using",
 293             suggestion,
 294             Applicability::MachineApplicable,
 295         );
 296     }
 297 }
 298
 299 fn check_powi(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args: &[Expr<'_>]) {
 300     if let Some((value, _)) = constant(cx, cx.typeck_results(), &args[0]) {
 301         if value == Int(2) {
 302             if let Some(parent) = get_parent_expr(cx, expr) {
 303                 if let Some(grandparent) = get_parent_expr(cx, parent) {
 304                     if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, receiver, ..) = grandparent.kind
 305                     {
 306                         if method_name.as_str() == "sqrt" && detect_hypot(cx, receiver).is_some() {
 307                             return;
 308                         }
 309                     }
 310                 }
 311
 312                 if let ExprKind::Binary(
 313                     Spanned {
 314                         node: op @ (BinOpKind::Add | BinOpKind::Sub),
 315                         ..
 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                     // Negate expr if original code has subtraction and expr is on the right side
 324                     let maybe_neg_sugg = |expr, hir_id| {
 325                         let sugg = Sugg::hir(cx, expr, "..");
 326                         if matches!(op, BinOpKind::Sub) && hir_id == rhs.hir_id {
 327                             format!("-{sugg}")
 328                         } else {
 329                             sugg.to_string()
 330                         }
 331                     };
 332
 333                     span_lint_and_sugg(
 334                         cx,
 335                         SUBOPTIMAL_FLOPS,
 336                         parent.span,
 337                         "multiply and add expressions can be calculated more efficiently and accurately",
 338                         "consider using",
 339                         format!(
 340                             "{}.mul_add({}, {})",
 341                             Sugg::hir(cx, receiver, "..").maybe_par(),
 342                             maybe_neg_sugg(receiver, expr.hir_id),
 343                             maybe_neg_sugg(other_addend, other_addend.hir_id),
 344                         ),
 345                         Applicability::MachineApplicable,
 346                     );
 347                 }
 348             }
 349         }
 350     }
 351 }
 352
 353 fn detect_hypot(cx: &LateContext<'_>, receiver: &Expr<'_>) -> Option<String> {
 354     if let ExprKind::Binary(
 355         Spanned {
 356             node: BinOpKind::Add, ..
 357         },
 358         add_lhs,
 359         add_rhs,
 360     ) = receiver.kind
 361     {
 362         // check if expression of the form x * x + y * y
 363         if_chain! {
 364             if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, lmul_lhs, lmul_rhs) = add_lhs.kind;
 365             if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, rmul_lhs, rmul_rhs) = add_rhs.kind;
 366             if eq_expr_value(cx, lmul_lhs, lmul_rhs);
 367             if eq_expr_value(cx, rmul_lhs, rmul_rhs);
 368             then {
 369                 return Some(format!("{}.hypot({})", Sugg::hir(cx, lmul_lhs, "..").maybe_par(), Sugg::hir(cx, rmul_lhs, "..")));
 370             }
 371         }
 372
 373         // check if expression of the form x.powi(2) + y.powi(2)
 374         if_chain! {
 375             if let ExprKind::MethodCall(
 376                 PathSegment { ident: lmethod_name, .. },
 377                 largs_0, [largs_1, ..],
 378                 _
 379             ) = &add_lhs.kind;
 380             if let ExprKind::MethodCall(
 381                 PathSegment { ident: rmethod_name, .. },
 382                 rargs_0, [rargs_1, ..],
 383                 _
 384             ) = &add_rhs.kind;
 385             if lmethod_name.as_str() == "powi" && rmethod_name.as_str() == "powi";
 386             if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), largs_1);
 387             if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), rargs_1);
 388             if Int(2) == lvalue && Int(2) == rvalue;
 389             then {
 390                 return Some(format!("{}.hypot({})", Sugg::hir(cx, largs_0, "..").maybe_par(), Sugg::hir(cx, rargs_0, "..")));
 391             }
 392         }
 393     }
 394
 395     None
 396 }
 397
 398 fn check_hypot(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>) {
 399     if let Some(message) = detect_hypot(cx, receiver) {
 400         span_lint_and_sugg(
 401             cx,
 402             IMPRECISE_FLOPS,
 403             expr.span,
 404             "hypotenuse can be computed more accurately",
 405             "consider using",
 406             message,
 407             Applicability::MachineApplicable,
 408         );
 409     }
 410 }
 411
 412 // TODO: Lint expressions of the form `x.exp() - y` where y > 1
 413 // and suggest usage of `x.exp_m1() - (y - 1)` instead
 414 fn check_expm1(cx: &LateContext<'_>, expr: &Expr<'_>) {
 415     if_chain! {
 416         if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, lhs, rhs) = expr.kind;
 417         if cx.typeck_results().expr_ty(lhs).is_floating_point();
 418         if let Some((value, _)) = constant(cx, cx.typeck_results(), rhs);
 419         if F32(1.0) == value || F64(1.0) == value;
 420         if let ExprKind::MethodCall(path, self_arg, ..) = &lhs.kind;
 421         if cx.typeck_results().expr_ty(self_arg).is_floating_point();
 422         if path.ident.name.as_str() == "exp";
 423         then {
 424             span_lint_and_sugg(
 425                 cx,
 426                 IMPRECISE_FLOPS,
 427                 expr.span,
 428                 "(e.pow(x) - 1) can be computed more accurately",
 429                 "consider using",
 430                 format!(
 431                     "{}.exp_m1()",
 432                     Sugg::hir(cx, self_arg, "..").maybe_par()
 433                 ),
 434                 Applicability::MachineApplicable,
 435             );
 436         }
 437     }
 438 }
 439
 440 fn is_float_mul_expr<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
 441     if_chain! {
 442         if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, lhs, rhs) = &expr.kind;
 443         if cx.typeck_results().expr_ty(lhs).is_floating_point();
 444         if cx.typeck_results().expr_ty(rhs).is_floating_point();
 445         then {
 446             return Some((lhs, rhs));
 447         }
 448     }
 449
 450     None
 451 }
 452
 453 // TODO: Fix rust-lang/rust-clippy#4735
 454 fn check_mul_add(cx: &LateContext<'_>, expr: &Expr<'_>) {
 455     if let ExprKind::Binary(
 456         Spanned {
 457             node: op @ (BinOpKind::Add | BinOpKind::Sub),
 458             ..
 459         },
 460         lhs,
 461         rhs,
 462     ) = &expr.kind
 463     {
 464         if let Some(parent) = get_parent_expr(cx, expr) {
 465             if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, receiver, ..) = parent.kind {
 466                 if method_name.as_str() == "sqrt" && detect_hypot(cx, receiver).is_some() {
 467                     return;
 468                 }
 469             }
 470         }
 471
 472         let maybe_neg_sugg = |expr| {
 473             let sugg = Sugg::hir(cx, expr, "..");
 474             if let BinOpKind::Sub = op {
 475                 format!("-{sugg}")
 476             } else {
 477                 sugg.to_string()
 478             }
 479         };
 480
 481         let (recv, arg1, arg2) = if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, lhs) {
 482             (
 483                 inner_lhs,
 484                 Sugg::hir(cx, inner_rhs, "..").to_string(),
 485                 maybe_neg_sugg(rhs),
 486             )
 487         } else if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, rhs) {
 488             (
 489                 inner_lhs,
 490                 maybe_neg_sugg(inner_rhs),
 491                 Sugg::hir(cx, lhs, "..").to_string(),
 492             )
 493         } else {
 494             return;
 495         };
 496
 497         span_lint_and_sugg(
 498             cx,
 499             SUBOPTIMAL_FLOPS,
 500             expr.span,
 501             "multiply and add expressions can be calculated more efficiently and accurately",
 502             "consider using",
 503             format!("{}.mul_add({arg1}, {arg2})", prepare_receiver_sugg(cx, recv)),
 504             Applicability::MachineApplicable,
 505         );
 506     }
 507 }
 508
 509 /// Returns true iff expr is an expression which tests whether or not
 510 /// test is positive or an expression which tests whether or not test
 511 /// is nonnegative.
 512 /// Used for check-custom-abs function below
 513 fn is_testing_positive(cx: &LateContext<'_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
 514     if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
 515         match op {
 516             BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, right) && eq_expr_value(cx, left, test),
 517             BinOpKind::Lt | BinOpKind::Le => is_zero(cx, left) && eq_expr_value(cx, right, test),
 518             _ => false,
 519         }
 520     } else {
 521         false
 522     }
 523 }
 524
 525 /// See [`is_testing_positive`]
 526 fn is_testing_negative(cx: &LateContext<'_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
 527     if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
 528         match op {
 529             BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, left) && eq_expr_value(cx, right, test),
 530             BinOpKind::Lt | BinOpKind::Le => is_zero(cx, right) && eq_expr_value(cx, left, test),
 531             _ => false,
 532         }
 533     } else {
 534         false
 535     }
 536 }
 537
 538 /// Returns true iff expr is some zero literal
 539 fn is_zero(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 540     match constant_simple(cx, cx.typeck_results(), expr) {
 541         Some(Constant::Int(i)) => i == 0,
 542         Some(Constant::F32(f)) => f == 0.0,
 543         Some(Constant::F64(f)) => f == 0.0,
 544         _ => false,
 545     }
 546 }
 547
 548 /// If the two expressions are negations of each other, then it returns
 549 /// a tuple, in which the first element is true iff expr1 is the
 550 /// positive expressions, and the second element is the positive
 551 /// one of the two expressions
 552 /// If the two expressions are not negations of each other, then it
 553 /// returns None.
 554 fn are_negated<'a>(cx: &LateContext<'_>, expr1: &'a Expr<'a>, expr2: &'a Expr<'a>) -> Option<(bool, &'a Expr<'a>)> {
 555     if let ExprKind::Unary(UnOp::Neg, expr1_negated) = &expr1.kind {
 556         if eq_expr_value(cx, expr1_negated, expr2) {
 557             return Some((false, expr2));
 558         }
 559     }
 560     if let ExprKind::Unary(UnOp::Neg, expr2_negated) = &expr2.kind {
 561         if eq_expr_value(cx, expr1, expr2_negated) {
 562             return Some((true, expr1));
 563         }
 564     }
 565     None
 566 }
 567
 568 fn check_custom_abs(cx: &LateContext<'_>, expr: &Expr<'_>) {
 569     if_chain! {
 570         if let Some(higher::If { cond, then, r#else: Some(r#else) }) = higher::If::hir(expr);
 571         let if_body_expr = peel_blocks(then);
 572         let else_body_expr = peel_blocks(r#else);
 573         if let Some((if_expr_positive, body)) = are_negated(cx, if_body_expr, else_body_expr);
 574         then {
 575             let positive_abs_sugg = (
 576                 "manual implementation of `abs` method",
 577                 format!("{}.abs()", Sugg::hir(cx, body, "..").maybe_par()),
 578             );
 579             let negative_abs_sugg = (
 580                 "manual implementation of negation of `abs` method",
 581                 format!("-{}.abs()", Sugg::hir(cx, body, "..").maybe_par()),
 582             );
 583             let sugg = if is_testing_positive(cx, cond, body) {
 584                 if if_expr_positive {
 585                     positive_abs_sugg
 586                 } else {
 587                     negative_abs_sugg
 588                 }
 589             } else if is_testing_negative(cx, cond, body) {
 590                 if if_expr_positive {
 591                     negative_abs_sugg
 592                 } else {
 593                     positive_abs_sugg
 594                 }
 595             } else {
 596                 return;
 597             };
 598             span_lint_and_sugg(
 599                 cx,
 600                 SUBOPTIMAL_FLOPS,
 601                 expr.span,
 602                 sugg.0,
 603                 "try",
 604                 sugg.1,
 605                 Applicability::MachineApplicable,
 606             );
 607         }
 608     }
 609 }
 610
 611 fn are_same_base_logs(cx: &LateContext<'_>, expr_a: &Expr<'_>, expr_b: &Expr<'_>) -> bool {
 612     if_chain! {
 613         if let ExprKind::MethodCall(PathSegment { ident: method_name_a, .. }, _, args_a, _) = expr_a.kind;
 614         if let ExprKind::MethodCall(PathSegment { ident: method_name_b, .. }, _, args_b, _) = expr_b.kind;
 615         then {
 616             return method_name_a.as_str() == method_name_b.as_str() &&
 617                 args_a.len() == args_b.len() &&
 618                 (
 619                     ["ln", "log2", "log10"].contains(&method_name_a.as_str()) ||
 620                     method_name_a.as_str() == "log" && args_a.len() == 1 && eq_expr_value(cx, &args_a[0], &args_b[0])
 621                 );
 622         }
 623     }
 624
 625     false
 626 }
 627
 628 fn check_log_division(cx: &LateContext<'_>, expr: &Expr<'_>) {
 629     // check if expression of the form x.logN() / y.logN()
 630     if_chain! {
 631         if let ExprKind::Binary(
 632             Spanned {
 633                 node: BinOpKind::Div, ..
 634             },
 635             lhs,
 636             rhs,
 637         ) = &expr.kind;
 638         if are_same_base_logs(cx, lhs, rhs);
 639         if let ExprKind::MethodCall(_, largs_self, ..) = &lhs.kind;
 640         if let ExprKind::MethodCall(_, rargs_self, ..) = &rhs.kind;
 641         then {
 642             span_lint_and_sugg(
 643                 cx,
 644                 SUBOPTIMAL_FLOPS,
 645                 expr.span,
 646                 "log base can be expressed more clearly",
 647                 "consider using",
 648                 format!("{}.log({})", Sugg::hir(cx, largs_self, "..").maybe_par(), Sugg::hir(cx, rargs_self, ".."),),
 649                 Applicability::MachineApplicable,
 650             );
 651         }
 652     }
 653 }
 654
 655 fn check_radians(cx: &LateContext<'_>, expr: &Expr<'_>) {
 656     if_chain! {
 657         if let ExprKind::Binary(
 658             Spanned {
 659                 node: BinOpKind::Div, ..
 660             },
 661             div_lhs,
 662             div_rhs,
 663         ) = &expr.kind;
 664         if let ExprKind::Binary(
 665             Spanned {
 666                 node: BinOpKind::Mul, ..
 667             },
 668             mul_lhs,
 669             mul_rhs,
 670         ) = &div_lhs.kind;
 671         if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), div_rhs);
 672         if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), mul_rhs);
 673         then {
 674             // TODO: also check for constant values near PI/180 or 180/PI
 675             if (F32(f32_consts::PI) == rvalue || F64(f64_consts::PI) == rvalue) &&
 676                (F32(180_f32) == lvalue || F64(180_f64) == lvalue)
 677             {
 678                 let mut proposal = format!("{}.to_degrees()", Sugg::hir(cx, mul_lhs, "..").maybe_par());
 679                 if_chain! {
 680                     if let ExprKind::Lit(ref literal) = mul_lhs.kind;
 681                     if let ast::LitKind::Float(ref value, float_type) = literal.node;
 682                     if float_type == ast::LitFloatType::Unsuffixed;
 683                     then {
 684                         if value.as_str().ends_with('.') {
 685                             proposal = format!("{}0_f64.to_degrees()", Sugg::hir(cx, mul_lhs, ".."));
 686                         } else {
 687                             proposal = format!("{}_f64.to_degrees()", Sugg::hir(cx, mul_lhs, ".."));
 688                         }
 689                     }
 690                 }
 691                 span_lint_and_sugg(
 692                     cx,
 693                     SUBOPTIMAL_FLOPS,
 694                     expr.span,
 695                     "conversion to degrees can be done more accurately",
 696                     "consider using",
 697                     proposal,
 698                     Applicability::MachineApplicable,
 699                 );
 700             } else if
 701                 (F32(180_f32) == rvalue || F64(180_f64) == rvalue) &&
 702                 (F32(f32_consts::PI) == lvalue || F64(f64_consts::PI) == lvalue)
 703             {
 704                 let mut proposal = format!("{}.to_radians()", Sugg::hir(cx, mul_lhs, "..").maybe_par());
 705                 if_chain! {
 706                     if let ExprKind::Lit(ref literal) = mul_lhs.kind;
 707                     if let ast::LitKind::Float(ref value, float_type) = literal.node;
 708                     if float_type == ast::LitFloatType::Unsuffixed;
 709                     then {
 710                         if value.as_str().ends_with('.') {
 711                             proposal = format!("{}0_f64.to_radians()", Sugg::hir(cx, mul_lhs, ".."));
 712                         } else {
 713                             proposal = format!("{}_f64.to_radians()", Sugg::hir(cx, mul_lhs, ".."));
 714                         }
 715                     }
 716                 }
 717                 span_lint_and_sugg(
 718                     cx,
 719                     SUBOPTIMAL_FLOPS,
 720                     expr.span,
 721                     "conversion to radians can be done more accurately",
 722                     "consider using",
 723                     proposal,
 724                     Applicability::MachineApplicable,
 725                 );
 726             }
 727         }
 728     }
 729 }
 730
 731 impl<'tcx> LateLintPass<'tcx> for FloatingPointArithmetic {
 732     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 733         // All of these operations are currently not const.
 734         if in_constant(cx, expr.hir_id) {
 735             return;
 736         }
 737
 738         if let ExprKind::MethodCall(path, receiver, args, _) = &expr.kind {
 739             let recv_ty = cx.typeck_results().expr_ty(receiver);
 740
 741             if recv_ty.is_floating_point() {
 742                 match path.ident.name.as_str() {
 743                     "ln" => check_ln1p(cx, expr, receiver),
 744                     "log" => check_log_base(cx, expr, receiver, args),
 745                     "powf" => check_powf(cx, expr, receiver, args),
 746                     "powi" => check_powi(cx, expr, receiver, args),
 747                     "sqrt" => check_hypot(cx, expr, receiver),
 748                     _ => {},
 749                 }
 750             }
 751         } else {
 752             check_expm1(cx, expr);
 753             check_mul_add(cx, expr);
 754             check_custom_abs(cx, expr);
 755             check_log_division(cx, expr);
 756             check_radians(cx, expr);
 757         }
 758     }
 759 }