| // origin: FreeBSD /usr/src/lib/msun/src/s_cos.c */ |
| // |
| // ==================================================== |
| // Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
| // |
| // Developed at SunPro, a Sun Microsystems, Inc. business. |
| // Permission to use, copy, modify, and distribute this |
| // software is freely granted, provided that this notice |
| // is preserved. |
| // ==================================================== |
| |
| use super::{k_cos, k_sin, rem_pio2}; |
| |
| // cos(x) |
| // Return cosine function of x. |
| // |
| // kernel function: |
| // k_sin ... sine function on [-pi/4,pi/4] |
| // k_cos ... cosine function on [-pi/4,pi/4] |
| // rem_pio2 ... argument reduction routine |
| // |
| // Method. |
| // Let S,C and T denote the sin, cos and tan respectively on |
| // [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 |
| // in [-pi/4 , +pi/4], and let n = k mod 4. |
| // We have |
| // |
| // n sin(x) cos(x) tan(x) |
| // ---------------------------------------------------------- |
| // 0 S C T |
| // 1 C -S -1/T |
| // 2 -S -C T |
| // 3 -C S -1/T |
| // ---------------------------------------------------------- |
| // |
| // Special cases: |
| // Let trig be any of sin, cos, or tan. |
| // trig(+-INF) is NaN, with signals; |
| // trig(NaN) is that NaN; |
| // |
| // Accuracy: |
| // TRIG(x) returns trig(x) nearly rounded |
| // |
| #[inline] |
| #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] |
| pub fn cos(x: f64) -> f64 { |
| let ix = (f64::to_bits(x) >> 32) as u32 & 0x7fffffff; |
| |
| /* |x| ~< pi/4 */ |
| if ix <= 0x3fe921fb { |
| if ix < 0x3e46a09e { |
| /* if x < 2**-27 * sqrt(2) */ |
| /* raise inexact if x != 0 */ |
| if x as i32 == 0 { |
| return 1.0; |
| } |
| } |
| return k_cos(x, 0.0); |
| } |
| |
| /* cos(Inf or NaN) is NaN */ |
| if ix >= 0x7ff00000 { |
| return x - x; |
| } |
| |
| /* argument reduction needed */ |
| let (n, y0, y1) = rem_pio2(x); |
| match n & 3 { |
| 0 => k_cos(y0, y1), |
| 1 => -k_sin(y0, y1, 1), |
| 2 => -k_cos(y0, y1), |
| _ => k_sin(y0, y1, 1), |
| } |
| } |
