2 constant, constant_simple, Constant,
5 use crate::utils::{higher, numeric_literal, span_lint_and_sugg, sugg, SpanlessEq};
6 use if_chain::if_chain;
7 use rustc_errors::Applicability;
8 use rustc_hir::{BinOpKind, Expr, ExprKind, UnOp};
9 use rustc_lint::{LateContext, LateLintPass};
11 use rustc_session::{declare_lint_pass, declare_tool_lint};
12 use rustc_span::source_map::Spanned;
15 use std::f32::consts as f32_consts;
16 use std::f64::consts as f64_consts;
19 declare_clippy_lint! {
20 /// **What it does:** Looks for floating-point expressions that
21 /// can be expressed using built-in methods to improve accuracy
22 /// at the cost of performance.
24 /// **Why is this bad?** Negatively impacts accuracy.
26 /// **Known problems:** None
33 /// let _ = a.powf(1.0 / 3.0);
34 /// let _ = (1.0 + a).ln();
35 /// let _ = a.exp() - 1.0;
38 /// is better expressed as
44 /// let _ = a.ln_1p();
45 /// let _ = a.exp_m1();
49 "usage of imprecise floating point operations"
52 declare_clippy_lint! {
53 /// **What it does:** Looks for floating-point expressions that
54 /// can be expressed using built-in methods to improve both
55 /// accuracy and performance.
57 /// **Why is this bad?** Negatively impacts accuracy and performance.
59 /// **Known problems:** None
64 /// use std::f32::consts::E;
67 /// let _ = (2f32).powf(a);
68 /// let _ = E.powf(a);
69 /// let _ = a.powf(1.0 / 2.0);
70 /// let _ = a.log(2.0);
71 /// let _ = a.log(10.0);
73 /// let _ = a.powf(2.0);
74 /// let _ = a * 2.0 + 4.0;
75 /// let _ = if a < 0.0 {
80 /// let _ = if a < 0.0 {
87 /// is better expressed as
90 /// use std::f32::consts::E;
97 /// let _ = a.log10();
99 /// let _ = a.powi(2);
100 /// let _ = a.mul_add(2.0, 4.0);
102 /// let _ = -a.abs();
104 pub SUBOPTIMAL_FLOPS,
106 "usage of sub-optimal floating point operations"
109 declare_lint_pass!(FloatingPointArithmetic => [
114 // Returns the specialized log method for a given base if base is constant
115 // and is one of 2, 10 and e
116 fn get_specialized_log_method(cx: &LateContext<'_, '_>, base: &Expr<'_>) -> Option<&'static str> {
117 if let Some((value, _)) = constant(cx, cx.tables, base) {
118 if F32(2.0) == value || F64(2.0) == value {
120 } else if F32(10.0) == value || F64(10.0) == value {
121 return Some("log10");
122 } else if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
130 // Adds type suffixes and parenthesis to method receivers if necessary
131 fn prepare_receiver_sugg<'a>(cx: &LateContext<'_, '_>, mut expr: &'a Expr<'a>) -> Sugg<'a> {
132 let mut suggestion = Sugg::hir(cx, expr, "..");
134 if let ExprKind::Unary(UnOp::UnNeg, inner_expr) = &expr.kind {
139 // if the expression is a float literal and it is unsuffixed then
140 // add a suffix so the suggestion is valid and unambiguous
141 if let ty::Float(float_ty) = cx.tables.expr_ty(expr).kind;
142 if let ExprKind::Lit(lit) = &expr.kind;
143 if let ast::LitKind::Float(sym, ast::LitFloatType::Unsuffixed) = lit.node;
148 // Check for float literals without numbers following the decimal
149 // separator such as `2.` and adds a trailing zero
150 if sym.as_str().ends_with('.') {
158 suggestion = match suggestion {
159 Sugg::MaybeParen(_) => Sugg::MaybeParen(op),
160 _ => Sugg::NonParen(op)
165 suggestion.maybe_par()
168 fn check_log_base(cx: &LateContext<'_, '_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
169 if let Some(method) = get_specialized_log_method(cx, &args[1]) {
174 "logarithm for bases 2, 10 and e can be computed more accurately",
176 format!("{}.{}()", Sugg::hir(cx, &args[0], ".."), method),
177 Applicability::MachineApplicable,
182 // TODO: Lint expressions of the form `(x + y).ln()` where y > 1 and
183 // suggest usage of `(x + (y - 1)).ln_1p()` instead
184 fn check_ln1p(cx: &LateContext<'_, '_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
185 if let ExprKind::Binary(
187 node: BinOpKind::Add, ..
193 let recv = match (constant(cx, cx.tables, lhs), constant(cx, cx.tables, rhs)) {
194 (Some((value, _)), _) if F32(1.0) == value || F64(1.0) == value => rhs,
195 (_, Some((value, _))) if F32(1.0) == value || F64(1.0) == value => lhs,
203 "ln(1 + x) can be computed more accurately",
205 format!("{}.ln_1p()", prepare_receiver_sugg(cx, recv)),
206 Applicability::MachineApplicable,
211 // Returns an integer if the float constant is a whole number and it can be
212 // converted to an integer without loss of precision. For now we only check
213 // ranges [-16777215, 16777216) for type f32 as whole number floats outside
214 // this range are lossy and ambiguous.
215 #[allow(clippy::cast_possible_truncation)]
216 fn get_integer_from_float_constant(value: &Constant) -> Option<i32> {
218 F32(num) if num.fract() == 0.0 => {
219 if (-16_777_215.0..16_777_216.0).contains(num) {
220 Some(num.round() as i32)
225 F64(num) if num.fract() == 0.0 => {
226 if (-2_147_483_648.0..2_147_483_648.0).contains(num) {
227 Some(num.round() as i32)
236 fn check_powf(cx: &LateContext<'_, '_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
238 if let Some((value, _)) = constant(cx, cx.tables, &args[0]) {
239 let method = if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
241 } else if F32(2.0) == value || F64(2.0) == value {
251 "exponent for bases 2 and e can be computed more accurately",
253 format!("{}.{}()", prepare_receiver_sugg(cx, &args[1]), method),
254 Applicability::MachineApplicable,
259 if let Some((value, _)) = constant(cx, cx.tables, &args[1]) {
260 let (lint, help, suggestion) = if F32(1.0 / 2.0) == value || F64(1.0 / 2.0) == value {
263 "square-root of a number can be computed more efficiently and accurately",
264 format!("{}.sqrt()", Sugg::hir(cx, &args[0], "..")),
266 } else if F32(1.0 / 3.0) == value || F64(1.0 / 3.0) == value {
269 "cube-root of a number can be computed more accurately",
270 format!("{}.cbrt()", Sugg::hir(cx, &args[0], "..")),
272 } else if let Some(exponent) = get_integer_from_float_constant(&value) {
275 "exponentiation with integer powers can be computed more efficiently",
278 Sugg::hir(cx, &args[0], ".."),
279 numeric_literal::format(&exponent.to_string(), None, false)
293 Applicability::MachineApplicable,
298 // TODO: Lint expressions of the form `x.exp() - y` where y > 1
299 // and suggest usage of `x.exp_m1() - (y - 1)` instead
300 fn check_expm1(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
302 if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, ref lhs, ref rhs) = expr.kind;
303 if cx.tables.expr_ty(lhs).is_floating_point();
304 if let Some((value, _)) = constant(cx, cx.tables, rhs);
305 if F32(1.0) == value || F64(1.0) == value;
306 if let ExprKind::MethodCall(ref path, _, ref method_args) = lhs.kind;
307 if cx.tables.expr_ty(&method_args[0]).is_floating_point();
308 if path.ident.name.as_str() == "exp";
314 "(e.pow(x) - 1) can be computed more accurately",
318 Sugg::hir(cx, &method_args[0], "..")
320 Applicability::MachineApplicable,
326 fn is_float_mul_expr<'a>(cx: &LateContext<'_, '_>, expr: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
328 if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, ref lhs, ref rhs) = &expr.kind;
329 if cx.tables.expr_ty(lhs).is_floating_point();
330 if cx.tables.expr_ty(rhs).is_floating_point();
332 return Some((lhs, rhs));
339 // TODO: Fix rust-lang/rust-clippy#4735
340 fn check_mul_add(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
341 if let ExprKind::Binary(
343 node: BinOpKind::Add, ..
349 let (recv, arg1, arg2) = if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, lhs) {
350 (inner_lhs, inner_rhs, rhs)
351 } else if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, rhs) {
352 (inner_lhs, inner_rhs, lhs)
361 "multiply and add expressions can be calculated more efficiently and accurately",
364 "{}.mul_add({}, {})",
365 prepare_receiver_sugg(cx, recv),
366 Sugg::hir(cx, arg1, ".."),
367 Sugg::hir(cx, arg2, ".."),
369 Applicability::MachineApplicable,
374 /// Returns true iff expr is an expression which tests whether or not
375 /// test is positive or an expression which tests whether or not test
377 /// Used for check-custom-abs function below
378 fn is_testing_positive(cx: &LateContext<'_, '_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
379 if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
381 BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, right) && are_exprs_equal(cx, left, test),
382 BinOpKind::Lt | BinOpKind::Le => is_zero(cx, left) && are_exprs_equal(cx, right, test),
390 /// See [`is_testing_positive`]
391 fn is_testing_negative(cx: &LateContext<'_, '_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
392 if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
394 BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, left) && are_exprs_equal(cx, right, test),
395 BinOpKind::Lt | BinOpKind::Le => is_zero(cx, right) && are_exprs_equal(cx, left, test),
403 fn are_exprs_equal(cx: &LateContext<'_, '_>, expr1: &Expr<'_>, expr2: &Expr<'_>) -> bool {
404 SpanlessEq::new(cx).ignore_fn().eq_expr(expr1, expr2)
407 /// Returns true iff expr is some zero literal
408 fn is_zero(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool {
409 match constant_simple(cx, cx.tables, expr) {
410 Some(Constant::Int(i)) => i == 0,
411 Some(Constant::F32(f)) => f == 0.0,
412 Some(Constant::F64(f)) => f == 0.0,
417 /// If the two expressions are negations of each other, then it returns
418 /// a tuple, in which the first element is true iff expr1 is the
419 /// positive expressions, and the second element is the positive
420 /// one of the two expressions
421 /// If the two expressions are not negations of each other, then it
423 fn are_negated<'a>(cx: &LateContext<'_, '_>, expr1: &'a Expr<'a>, expr2: &'a Expr<'a>) -> Option<(bool, &'a Expr<'a>)> {
424 if let ExprKind::Unary(UnOp::UnNeg, expr1_negated) = &expr1.kind {
425 if are_exprs_equal(cx, expr1_negated, expr2) {
426 return Some((false, expr2));
429 if let ExprKind::Unary(UnOp::UnNeg, expr2_negated) = &expr2.kind {
430 if are_exprs_equal(cx, expr1, expr2_negated) {
431 return Some((true, expr1));
437 fn check_custom_abs(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
439 if let Some((cond, body, Some(else_body))) = higher::if_block(&expr);
440 if let ExprKind::Block(block, _) = body.kind;
441 if block.stmts.is_empty();
442 if let Some(if_body_expr) = block.expr;
443 if let ExprKind::Block(else_block, _) = else_body.kind;
444 if else_block.stmts.is_empty();
445 if let Some(else_body_expr) = else_block.expr;
446 if let Some((if_expr_positive, body)) = are_negated(cx, if_body_expr, else_body_expr);
448 let positive_abs_sugg = (
449 "manual implementation of `abs` method",
450 format!("{}.abs()", Sugg::hir(cx, body, "..")),
452 let negative_abs_sugg = (
453 "manual implementation of negation of `abs` method",
454 format!("-{}.abs()", Sugg::hir(cx, body, "..")),
456 let sugg = if is_testing_positive(cx, cond, body) {
457 if if_expr_positive {
462 } else if is_testing_negative(cx, cond, body) {
463 if if_expr_positive {
478 Applicability::MachineApplicable,
484 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FloatingPointArithmetic {
485 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
486 if let ExprKind::MethodCall(ref path, _, args) = &expr.kind {
487 let recv_ty = cx.tables.expr_ty(&args[0]);
489 if recv_ty.is_floating_point() {
490 match &*path.ident.name.as_str() {
491 "ln" => check_ln1p(cx, expr, args),
492 "log" => check_log_base(cx, expr, args),
493 "powf" => check_powf(cx, expr, args),
498 check_expm1(cx, expr);
499 check_mul_add(cx, expr);
500 check_custom_abs(cx, expr);