45 lines
1.4 KiB
Rust
45 lines
1.4 KiB
Rust
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use super::rem_pio2_large;
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use core::f64;
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const TOINT : f64 = 1.5 / f64::EPSILON;
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/// 53 bits of 2/pi
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const INV_PIO2 : f64 = 6.36619772367581382433e-01; /* 0x3FE45F30, 0x6DC9C883 */
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/// first 25 bits of pi/2
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const PIO2_1 : f64 = 1.57079631090164184570e+00; /* 0x3FF921FB, 0x50000000 */
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/// pi/2 - pio2_1
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const PIO2_1T : f64 = 1.58932547735281966916e-08; /* 0x3E5110b4, 0x611A6263 */
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/// Return the remainder of x rem pi/2 in *y
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///
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/// use double precision for everything except passing x
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/// use __rem_pio2_large() for large x
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#[inline]
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pub(crate) fn rem_pio2f(x : f32) -> (i32, f64) {
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let x64 = x as f64;
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let mut tx : [f64; 1] = [0.,];
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let mut ty : [f64; 1] = [0.,];
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let ix = x.to_bits() & 0x7fffffff;
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/* 25+53 bit pi is good enough for medium size */
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if ix < 0x4dc90fdb { /* |x| ~< 2^28*(pi/2), medium size */
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/* Use a specialized rint() to get fn. Assume round-to-nearest. */
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let f_n = x64*INV_PIO2 + TOINT - TOINT;
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return (f_n as i32, x64 - f_n*PIO2_1 - f_n*PIO2_1T);
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}
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if ix>=0x7f800000 { /* x is inf or NaN */
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return (0, x64-x64);
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}
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/* scale x into [2^23, 2^24-1] */
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let sign = (x.to_bits() >> 31) != 0;
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let e0 = ((ix>>23) - (0x7f+23)) as i32; /* e0 = ilogb(|x|)-23, positive */
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tx[0] = f32::from_bits(ix - (e0<<23) as u32) as f64;
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let n = rem_pio2_large(&tx, &mut ty, e0, 0);
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if sign {
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return (-n, -ty[0]);
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}
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(n, ty[0])
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}
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