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