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// Ported from musl, which is licensed under the MIT license:
// https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
//
// https://git.musl-libc.org/cgit/musl/tree/src/math/__rem_pio2f.c
const std = @import("std");
const rem_pio2_large = @import("rem_pio2_large.zig").rem_pio2_large;
const math = std.math;
const toint = 1.5 / math.floatEps(f64);
// pi/4
const pio4 = 0x1.921fb6p-1;
// invpio2: 53 bits of 2/pi
const invpio2 = 6.36619772367581382433e-01; // 0x3FE45F30, 0x6DC9C883
// pio2_1: first 25 bits of pi/2
const pio2_1 = 1.57079631090164184570e+00; // 0x3FF921FB, 0x50000000
// pio2_1t: pi/2 - pio2_1
const pio2_1t = 1.58932547735281966916e-08; // 0x3E5110b4, 0x611A6263
// Returns the remainder of x rem pi/2 in *y
// use double precision for everything except passing x
// use rem_pio2_large() for large x
pub fn rem_pio2f(x: f32, y: *f64) i32 {
var tx: [1]f64 = undefined;
var ty: [1]f64 = undefined;
var @"fn": f64 = undefined;
var ix: u32 = undefined;
var n: i32 = undefined;
var sign: bool = undefined;
var e0: u32 = undefined;
var ui: u32 = undefined;
ui = @bitCast(u32, x);
ix = ui & 0x7fffffff;
// 25+53 bit pi is good enough for medium size
if (ix < 0x4dc90fdb) { // |x| ~< 2^28*(pi/2), medium size
// Use a specialized rint() to get fn.
@"fn" = @floatCast(f64, x) * invpio2 + toint - toint;
n = @floatToInt(i32, @"fn");
y.* = x - @"fn" * pio2_1 - @"fn" * pio2_1t;
// Matters with directed rounding.
if (y.* < -pio4) {
n -= 1;
@"fn" -= 1;
y.* = x - @"fn" * pio2_1 - @"fn" * pio2_1t;
} else if (y.* > pio4) {
n += 1;
@"fn" += 1;
y.* = x - @"fn" * pio2_1 - @"fn" * pio2_1t;
}
return n;
}
if (ix >= 0x7f800000) { // x is inf or NaN
y.* = x - x;
return 0;
}
// scale x into [2^23, 2^24-1]
sign = ui >> 31 != 0;
e0 = (ix >> 23) - (0x7f + 23); // e0 = ilogb(|x|)-23, positive
ui = ix - (e0 << 23);
tx[0] = @bitCast(f32, ui);
n = rem_pio2_large(&tx, &ty, @intCast(i32, e0), 1, 0);
if (sign) {
y.* = -ty[0];
return -n;
}
y.* = ty[0];
return n;
}
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