Lokathor
64 lines
1.6 KiB
Rust
64 lines
1.6 KiB
Rust
use core::f64;
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const TOINT: f64 = 1. / f64::EPSILON;
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/// Ceil (f64)
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///
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/// Finds the nearest integer greater than or equal to `x`.
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#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
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pub fn ceil(x: f64) -> f64 {
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// On wasm32 we know that LLVM's intrinsic will compile to an optimized
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// `f64.ceil` native instruction, so we can leverage this for both code size
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// and speed.
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llvm_intrinsically_optimized! {
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#[cfg(target_arch = "wasm32")] {
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return unsafe { ::core::intrinsics::ceilf64(x) }
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}
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}
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let u: u64 = x.to_bits();
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let e: i64 = (u >> 52 & 0x7ff) as i64;
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let y: f64;
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if e >= 0x3ff + 52 || x == 0. {
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return x;
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}
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// y = int(x) - x, where int(x) is an integer neighbor of x
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y = if (u >> 63) != 0 {
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x - TOINT + TOINT - x
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} else {
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x + TOINT - TOINT - x
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};
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// special case because of non-nearest rounding modes
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if e < 0x3ff {
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force_eval!(y);
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return if (u >> 63) != 0 { -0. } else { 1. };
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}
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if y < 0. {
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x + y + 1.
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} else {
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x + y
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use core::f64::*;
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#[test]
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fn sanity_check() {
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assert_eq!(ceil(1.1), 2.0);
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assert_eq!(ceil(2.9), 3.0);
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}
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/// The spec: https://en.cppreference.com/w/cpp/numeric/math/ceil
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#[test]
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fn spec_tests() {
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// Not Asserted: that the current rounding mode has no effect.
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assert!(ceil(NAN).is_nan());
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for f in [0.0, -0.0, INFINITY, NEG_INFINITY].iter().copied() {
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assert_eq!(ceil(f), f);
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}
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}
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}
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