68 lines
2.3 KiB
Rust
68 lines
2.3 KiB
Rust
use rustc::lint::*;
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use rustc_front::hir::*;
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use std::f64::consts as f64;
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use utils::span_lint;
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use syntax::ast::Lit_::*;
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use syntax::ast::Lit;
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use syntax::ast::FloatTy::*;
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declare_lint! {
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pub APPROX_CONSTANT,
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Warn,
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"the approximate of a known float constant (in `std::f64::consts` or `std::f32::consts`) \
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is found; suggests to use the constant"
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}
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const KNOWN_CONSTS : &'static [(f64, &'static str)] = &[(f64::E, "E"), (f64::FRAC_1_PI, "FRAC_1_PI"),
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(f64::FRAC_1_SQRT_2, "FRAC_1_SQRT_2"), (f64::FRAC_2_PI, "FRAC_2_PI"),
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(f64::FRAC_2_SQRT_PI, "FRAC_2_SQRT_PI"), (f64::FRAC_PI_2, "FRAC_PI_2"), (f64::FRAC_PI_3, "FRAC_PI_3"),
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(f64::FRAC_PI_4, "FRAC_PI_4"), (f64::FRAC_PI_6, "FRAC_PI_6"), (f64::FRAC_PI_8, "FRAC_PI_8"),
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(f64::LN_10, "LN_10"), (f64::LN_2, "LN_2"), (f64::LOG10_E, "LOG10_E"), (f64::LOG2_E, "LOG2_E"),
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(f64::PI, "PI"), (f64::SQRT_2, "SQRT_2")];
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const EPSILON_DIVISOR : f64 = 8192f64; //TODO: test to find a good value
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#[derive(Copy,Clone)]
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pub struct ApproxConstant;
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impl LintPass for ApproxConstant {
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fn get_lints(&self) -> LintArray {
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lint_array!(APPROX_CONSTANT)
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}
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}
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impl LateLintPass for ApproxConstant {
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fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
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if let &ExprLit(ref lit) = &e.node {
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check_lit(cx, lit, e);
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}
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}
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}
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fn check_lit(cx: &LateContext, lit: &Lit, e: &Expr) {
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match lit.node {
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LitFloat(ref str, TyF32) => check_known_consts(cx, e, str, "f32"),
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LitFloat(ref str, TyF64) => check_known_consts(cx, e, str, "f64"),
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LitFloatUnsuffixed(ref str) =>
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check_known_consts(cx, e, str, "f{32, 64}"),
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_ => ()
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}
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}
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fn check_known_consts(cx: &LateContext, e: &Expr, str: &str, module: &str) {
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if let Ok(value) = str.parse::<f64>() {
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for &(constant, name) in KNOWN_CONSTS {
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if !within_epsilon(constant, value) { continue; }
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span_lint(cx, APPROX_CONSTANT, e.span, &format!(
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"approximate value of `{}::{}` found. \
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Consider using it directly", module, &name));
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}
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}
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}
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fn within_epsilon(target: f64, value: f64) -> bool {
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f64::abs(value - target) < f64::abs(if target > value {
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target
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} else { value }) / EPSILON_DIVISOR
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}
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