253 lines
8.0 KiB
Rust
253 lines
8.0 KiB
Rust
use crate::consts::{
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constant, Constant,
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Constant::{F32, F64},
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};
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use crate::utils::*;
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use if_chain::if_chain;
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use rustc::declare_lint_pass;
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use rustc::hir::*;
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use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc_errors::Applicability;
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use rustc_session::declare_tool_lint;
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use std::f32::consts as f32_consts;
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use std::f64::consts as f64_consts;
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declare_clippy_lint! {
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/// **What it does:** Looks for floating-point expressions that
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/// can be expressed using built-in methods to improve accuracy,
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/// performance and/or succinctness.
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///
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/// **Why is this bad?** Negatively affects accuracy, performance
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/// and/or readability.
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///
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/// **Known problems:** None
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///
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/// **Example:**
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///
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/// ```rust
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/// use std::f32::consts::E;
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///
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/// let a = 3f32;
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/// let _ = (2f32).powf(a);
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/// let _ = E.powf(a);
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/// let _ = a.powf(1.0 / 2.0);
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/// let _ = a.powf(1.0 / 3.0);
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/// let _ = a.log(2.0);
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/// let _ = a.log(10.0);
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/// let _ = a.log(E);
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/// let _ = (1.0 + a).ln();
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/// let _ = a.exp() - 1.0;
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/// let _ = a.powf(2.0);
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/// ```
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///
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/// is better expressed as
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///
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/// ```rust
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/// use std::f32::consts::E;
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///
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/// let a = 3f32;
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/// let _ = a.exp2();
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/// let _ = a.exp();
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/// let _ = a.sqrt();
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/// let _ = a.cbrt();
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/// let _ = a.log2();
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/// let _ = a.log10();
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/// let _ = a.ln();
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/// let _ = a.ln_1p();
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/// let _ = a.exp_m1();
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/// let _ = a.powi(2);
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/// ```
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pub FLOATING_POINT_IMPROVEMENTS,
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nursery,
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"looks for improvements to floating-point expressions"
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}
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declare_lint_pass!(FloatingPointArithmetic => [FLOATING_POINT_IMPROVEMENTS]);
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fn check_log_base(cx: &LateContext<'_, '_>, expr: &Expr, args: &HirVec<Expr>) {
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let arg = sugg::Sugg::hir(cx, &args[0], "..").maybe_par();
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if let Some((value, _)) = constant(cx, cx.tables, &args[1]) {
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let method;
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if F32(2.0) == value || F64(2.0) == value {
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method = "log2";
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} else if F32(10.0) == value || F64(10.0) == value {
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method = "log10";
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} else if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
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method = "ln";
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} else {
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return;
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}
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span_lint_and_sugg(
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cx,
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FLOATING_POINT_IMPROVEMENTS,
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expr.span,
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"logarithm for bases 2, 10 and e can be computed more accurately",
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"consider using",
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format!("{}.{}()", arg, method),
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Applicability::MachineApplicable,
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);
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}
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}
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// TODO: Lint expressions of the form `(x + 1).ln()` and `(x + y).ln()`
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// where y > 1 and suggest usage of `(x + (y - 1)).ln_1p()` instead
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fn check_ln1p(cx: &LateContext<'_, '_>, expr: &Expr, args: &HirVec<Expr>) {
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if_chain! {
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if let ExprKind::Binary(op, ref lhs, ref rhs) = &args[0].kind;
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if op.node == BinOpKind::Add;
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if let Some((value, _)) = constant(cx, cx.tables, lhs);
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if F32(1.0) == value || F64(1.0) == value;
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then {
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let arg = sugg::Sugg::hir(cx, rhs, "..").maybe_par();
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span_lint_and_sugg(
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cx,
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FLOATING_POINT_IMPROVEMENTS,
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expr.span,
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"ln(1 + x) can be computed more accurately",
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"consider using",
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format!("{}.ln_1p()", arg),
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Applicability::MachineApplicable,
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);
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}
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}
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}
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// Returns an integer if the float constant is a whole number and it
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// can be converted to an integer without loss
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// TODO: Add a better check to determine whether the float can be
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// casted without loss
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#[allow(clippy::cast_possible_truncation)]
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fn get_integer_from_float_constant(value: &Constant) -> Option<i64> {
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match value {
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F32(num) if (num.trunc() - num).abs() <= std::f32::EPSILON => {
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if *num > -16_777_217.0 && *num < 16_777_217.0 {
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Some(num.round() as i64)
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} else {
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None
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}
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},
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F64(num) if (num.trunc() - num).abs() <= std::f64::EPSILON => {
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if *num > -9_007_199_254_740_993.0 && *num < 9_007_199_254_740_993.0 {
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Some(num.round() as i64)
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} else {
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None
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}
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},
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_ => None,
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}
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}
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fn check_powf(cx: &LateContext<'_, '_>, expr: &Expr, args: &HirVec<Expr>) {
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// Check receiver
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if let Some((value, _)) = constant(cx, cx.tables, &args[0]) {
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let method;
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if F32(f32_consts::E) == value || F64(f64_consts::E) == value {
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method = "exp";
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} else if F32(2.0) == value || F64(2.0) == value {
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method = "exp2";
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} else {
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return;
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}
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span_lint_and_sugg(
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cx,
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FLOATING_POINT_IMPROVEMENTS,
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expr.span,
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"exponent for bases 2 and e can be computed more accurately",
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"consider using",
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format!("{}.{}()", sugg::Sugg::hir(cx, &args[1], "..").maybe_par(), method),
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Applicability::MachineApplicable,
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);
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}
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// Check argument
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if let Some((value, _)) = constant(cx, cx.tables, &args[1]) {
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let help;
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let method;
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if F32(1.0 / 2.0) == value || F64(1.0 / 2.0) == value {
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help = "square-root of a number can be computed more efficiently and accurately";
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method = "sqrt";
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} else if F32(1.0 / 3.0) == value || F64(1.0 / 3.0) == value {
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help = "cube-root of a number can be computed more accurately";
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method = "cbrt";
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} else if let Some(exponent) = get_integer_from_float_constant(&value) {
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span_lint_and_sugg(
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cx,
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FLOATING_POINT_IMPROVEMENTS,
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expr.span,
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"exponentiation with integer powers can be computed more efficiently",
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"consider using",
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format!("{}.powi({})", sugg::Sugg::hir(cx, &args[0], ".."), exponent),
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Applicability::MachineApplicable,
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);
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return;
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} else {
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return;
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}
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span_lint_and_sugg(
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cx,
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FLOATING_POINT_IMPROVEMENTS,
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expr.span,
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help,
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"consider using",
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format!("{}.{}()", sugg::Sugg::hir(cx, &args[0], ".."), method),
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Applicability::MachineApplicable,
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);
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}
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}
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// TODO: Lint expressions of the form `x.exp() - y` where y > 1
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// and suggest usage of `x.exp_m1() - (y - 1)` instead
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fn check_expm1(cx: &LateContext<'_, '_>, expr: &Expr) {
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if_chain! {
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if let ExprKind::Binary(op, ref lhs, ref rhs) = expr.kind;
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if op.node == BinOpKind::Sub;
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if cx.tables.expr_ty(lhs).is_floating_point();
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if let Some((value, _)) = constant(cx, cx.tables, rhs);
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if F32(1.0) == value || F64(1.0) == value;
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if let ExprKind::MethodCall(ref path, _, ref method_args) = lhs.kind;
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if path.ident.name.as_str() == "exp";
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then {
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span_lint_and_sugg(
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cx,
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FLOATING_POINT_IMPROVEMENTS,
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expr.span,
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"(e.pow(x) - 1) can be computed more accurately",
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"consider using",
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format!(
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"{}.exp_m1()",
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sugg::Sugg::hir(cx, &method_args[0], "..")
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),
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Applicability::MachineApplicable,
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);
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}
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FloatingPointArithmetic {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if let ExprKind::MethodCall(ref path, _, args) = &expr.kind {
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let recv_ty = cx.tables.expr_ty(&args[0]);
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if recv_ty.is_floating_point() {
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match &*path.ident.name.as_str() {
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"ln" => check_ln1p(cx, expr, args),
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"log" => check_log_base(cx, expr, args),
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"powf" => check_powf(cx, expr, args),
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_ => {},
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}
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}
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} else {
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check_expm1(cx, expr);
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}
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}
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}
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