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
32 /// let _ = a.powf(1.0 / 3.0);
33 /// let _ = (1.0 + a).ln();
34 /// let _ = a.exp() - 1.0;
37 /// is better expressed as
42 /// let _ = a.ln_1p();
43 /// let _ = a.exp_m1();
47 "usage of imprecise floating point operations"
50 declare_clippy_lint! {
51 /// **What it does:** Looks for floating-point expressions that
52 /// can be expressed using built-in methods to improve both
53 /// accuracy and performance.
55 /// **Why is this bad?** Negatively impacts accuracy and performance.
57 /// **Known problems:** None
62 /// use std::f32::consts::E;
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);
71 /// let _ = a.powf(2.0);
72 /// let _ = a * 2.0 + 4.0;
73 /// let _ = if a < 0.0 {
78 /// let _ = if a < 0.0 {
85 /// is better expressed as
88 /// use std::f32::consts::E;
95 /// let _ = a.log10();
97 /// let _ = a.powi(2);
98 /// let _ = a.mul_add(2.0, 4.0);
100 /// let _ = -a.abs();
102 pub SUBOPTIMAL_FLOPS,
104 "usage of sub-optimal floating point operations"
107 declare_lint_pass!(FloatingPointArithmetic => [
112 // Returns the specialized log method for a given base if base is constant
113 // and is one of 2, 10 and e
114 fn get_specialized_log_method(cx: &LateContext<'_, '_>, base: &Expr<'_>) -> Option<&'static str> {
115 if let Some((value, _)) = constant(cx, cx.tables, base) {
116 if F32(2.0) == value || F64(2.0) == value {
118 } else if F32(10.0) == value || F64(10.0) == value {
119 return Some("log10");
120 } else if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
128 // Adds type suffixes and parenthesis to method receivers if necessary
129 fn prepare_receiver_sugg<'a>(cx: &LateContext<'_, '_>, mut expr: &'a Expr<'a>) -> Sugg<'a> {
130 let mut suggestion = Sugg::hir(cx, expr, "..");
132 if let ExprKind::Unary(UnOp::UnNeg, inner_expr) = &expr.kind {
137 // if the expression is a float literal and it is unsuffixed then
138 // add a suffix so the suggestion is valid and unambiguous
139 if let ty::Float(float_ty) = cx.tables.expr_ty(expr).kind;
140 if let ExprKind::Lit(lit) = &expr.kind;
141 if let ast::LitKind::Float(sym, ast::LitFloatType::Unsuffixed) = lit.node;
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('.') {
156 suggestion = match suggestion {
157 Sugg::MaybeParen(_) => Sugg::MaybeParen(op),
158 _ => Sugg::NonParen(op)
163 suggestion.maybe_par()
166 fn check_log_base(cx: &LateContext<'_, '_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
167 if let Some(method) = get_specialized_log_method(cx, &args[1]) {
172 "logarithm for bases 2, 10 and e can be computed more accurately",
174 format!("{}.{}()", Sugg::hir(cx, &args[0], ".."), method),
175 Applicability::MachineApplicable,
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<'_>, args: &[Expr<'_>]) {
183 if let ExprKind::Binary(
185 node: BinOpKind::Add, ..
191 let recv = match (constant(cx, cx.tables, lhs), constant(cx, cx.tables, rhs)) {
192 (Some((value, _)), _) if F32(1.0) == value || F64(1.0) == value => rhs,
193 (_, Some((value, _))) if F32(1.0) == value || F64(1.0) == value => lhs,
201 "ln(1 + x) can be computed more accurately",
203 format!("{}.ln_1p()", prepare_receiver_sugg(cx, recv)),
204 Applicability::MachineApplicable,
209 // Returns an integer if the float constant is a whole number and it can be
210 // converted to an integer without loss of precision. For now we only check
211 // ranges [-16777215, 16777216) for type f32 as whole number floats outside
212 // this range are lossy and ambiguous.
213 #[allow(clippy::cast_possible_truncation)]
214 fn get_integer_from_float_constant(value: &Constant) -> Option<i32> {
216 F32(num) if num.fract() == 0.0 => {
217 if (-16_777_215.0..16_777_216.0).contains(num) {
218 Some(num.round() as i32)
223 F64(num) if num.fract() == 0.0 => {
224 if (-2_147_483_648.0..2_147_483_648.0).contains(num) {
225 Some(num.round() as i32)
234 fn check_powf(cx: &LateContext<'_, '_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
236 if let Some((value, _)) = constant(cx, cx.tables, &args[0]) {
237 let method = if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
239 } else if F32(2.0) == value || F64(2.0) == value {
249 "exponent for bases 2 and e can be computed more accurately",
251 format!("{}.{}()", prepare_receiver_sugg(cx, &args[1]), method),
252 Applicability::MachineApplicable,
257 if let Some((value, _)) = constant(cx, cx.tables, &args[1]) {
258 let (lint, help, suggestion) = if F32(1.0 / 2.0) == value || F64(1.0 / 2.0) == value {
261 "square-root of a number can be computed more efficiently and accurately",
262 format!("{}.sqrt()", Sugg::hir(cx, &args[0], "..")),
264 } else if F32(1.0 / 3.0) == value || F64(1.0 / 3.0) == value {
267 "cube-root of a number can be computed more accurately",
268 format!("{}.cbrt()", Sugg::hir(cx, &args[0], "..")),
270 } else if let Some(exponent) = get_integer_from_float_constant(&value) {
273 "exponentiation with integer powers can be computed more efficiently",
276 Sugg::hir(cx, &args[0], ".."),
277 numeric_literal::format(&exponent.to_string(), None, false)
291 Applicability::MachineApplicable,
296 // TODO: Lint expressions of the form `x.exp() - y` where y > 1
297 // and suggest usage of `x.exp_m1() - (y - 1)` instead
298 fn check_expm1(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
300 if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, ref lhs, ref rhs) = expr.kind;
301 if cx.tables.expr_ty(lhs).is_floating_point();
302 if let Some((value, _)) = constant(cx, cx.tables, rhs);
303 if F32(1.0) == value || F64(1.0) == value;
304 if let ExprKind::MethodCall(ref path, _, ref method_args, _) = lhs.kind;
305 if cx.tables.expr_ty(&method_args[0]).is_floating_point();
306 if path.ident.name.as_str() == "exp";
312 "(e.pow(x) - 1) can be computed more accurately",
316 Sugg::hir(cx, &method_args[0], "..")
318 Applicability::MachineApplicable,
324 fn is_float_mul_expr<'a>(cx: &LateContext<'_, '_>, expr: &'a Expr<'a>) -> Option<(&'a Expr<'a>, &'a Expr<'a>)> {
326 if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, ref lhs, ref rhs) = &expr.kind;
327 if cx.tables.expr_ty(lhs).is_floating_point();
328 if cx.tables.expr_ty(rhs).is_floating_point();
330 return Some((lhs, rhs));
337 // TODO: Fix rust-lang/rust-clippy#4735
338 fn check_mul_add(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
339 if let ExprKind::Binary(
341 node: BinOpKind::Add, ..
347 let (recv, arg1, arg2) = if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, lhs) {
348 (inner_lhs, inner_rhs, rhs)
349 } else if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, rhs) {
350 (inner_lhs, inner_rhs, lhs)
359 "multiply and add expressions can be calculated more efficiently and accurately",
362 "{}.mul_add({}, {})",
363 prepare_receiver_sugg(cx, recv),
364 Sugg::hir(cx, arg1, ".."),
365 Sugg::hir(cx, arg2, ".."),
367 Applicability::MachineApplicable,
372 /// Returns true iff expr is an expression which tests whether or not
373 /// test is positive or an expression which tests whether or not test
375 /// Used for check-custom-abs function below
376 fn is_testing_positive(cx: &LateContext<'_, '_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
377 if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
379 BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, right) && are_exprs_equal(cx, left, test),
380 BinOpKind::Lt | BinOpKind::Le => is_zero(cx, left) && are_exprs_equal(cx, right, test),
388 /// See [`is_testing_positive`]
389 fn is_testing_negative(cx: &LateContext<'_, '_>, expr: &Expr<'_>, test: &Expr<'_>) -> bool {
390 if let ExprKind::Binary(Spanned { node: op, .. }, left, right) = expr.kind {
392 BinOpKind::Gt | BinOpKind::Ge => is_zero(cx, left) && are_exprs_equal(cx, right, test),
393 BinOpKind::Lt | BinOpKind::Le => is_zero(cx, right) && are_exprs_equal(cx, left, test),
401 fn are_exprs_equal(cx: &LateContext<'_, '_>, expr1: &Expr<'_>, expr2: &Expr<'_>) -> bool {
402 SpanlessEq::new(cx).ignore_fn().eq_expr(expr1, expr2)
405 /// Returns true iff expr is some zero literal
406 fn is_zero(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool {
407 match constant_simple(cx, cx.tables, expr) {
408 Some(Constant::Int(i)) => i == 0,
409 Some(Constant::F32(f)) => f == 0.0,
410 Some(Constant::F64(f)) => f == 0.0,
415 /// If the two expressions are negations of each other, then it returns
416 /// a tuple, in which the first element is true iff expr1 is the
417 /// positive expressions, and the second element is the positive
418 /// one of the two expressions
419 /// If the two expressions are not negations of each other, then it
421 fn are_negated<'a>(cx: &LateContext<'_, '_>, expr1: &'a Expr<'a>, expr2: &'a Expr<'a>) -> Option<(bool, &'a Expr<'a>)> {
422 if let ExprKind::Unary(UnOp::UnNeg, expr1_negated) = &expr1.kind {
423 if are_exprs_equal(cx, expr1_negated, expr2) {
424 return Some((false, expr2));
427 if let ExprKind::Unary(UnOp::UnNeg, expr2_negated) = &expr2.kind {
428 if are_exprs_equal(cx, expr1, expr2_negated) {
429 return Some((true, expr1));
435 fn check_custom_abs(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
437 if let Some((cond, body, Some(else_body))) = higher::if_block(&expr);
438 if let ExprKind::Block(block, _) = body.kind;
439 if block.stmts.is_empty();
440 if let Some(if_body_expr) = block.expr;
441 if let ExprKind::Block(else_block, _) = else_body.kind;
442 if else_block.stmts.is_empty();
443 if let Some(else_body_expr) = else_block.expr;
444 if let Some((if_expr_positive, body)) = are_negated(cx, if_body_expr, else_body_expr);
446 let positive_abs_sugg = (
447 "manual implementation of `abs` method",
448 format!("{}.abs()", Sugg::hir(cx, body, "..")),
450 let negative_abs_sugg = (
451 "manual implementation of negation of `abs` method",
452 format!("-{}.abs()", Sugg::hir(cx, body, "..")),
454 let sugg = if is_testing_positive(cx, cond, body) {
455 if if_expr_positive {
460 } else if is_testing_negative(cx, cond, body) {
461 if if_expr_positive {
476 Applicability::MachineApplicable,
482 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FloatingPointArithmetic {
483 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
484 if let ExprKind::MethodCall(ref path, _, args, _) = &expr.kind {
485 let recv_ty = cx.tables.expr_ty(&args[0]);
487 if recv_ty.is_floating_point() {
488 match &*path.ident.name.as_str() {
489 "ln" => check_ln1p(cx, expr, args),
490 "log" => check_log_base(cx, expr, args),
491 "powf" => check_powf(cx, expr, args),
496 check_expm1(cx, expr);
497 check_mul_add(cx, expr);
498 check_custom_abs(cx, expr);