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/* | ||
* ==================================================== | ||
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. | ||
* | ||
* Developed at SunSoft, a Sun Microsystems, Inc. business. | ||
* Permission to use, copy, modify, and distribute this | ||
* software is freely granted, provided that this notice | ||
* is preserved. | ||
* ==================================================== | ||
*/ | ||
module Cosine | ||
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from "runtime/unsafe/wasmf64" include WasmF64 | ||
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/* | ||
* Source: https://git.musl-libc.org/cgit/musl/tree/src/math/__cos.c | ||
* | ||
* kernel cos function on [-pi/4, pi/4], pi/4 ~ 0.785398164 | ||
* Input x is assumed to be bounded by ~pi/4 in magnitude. | ||
* Input y is the tail of x. | ||
* | ||
* Algorithm | ||
* 1. Since cos(-x) = cos(x), we need only to consider positive x. | ||
* 2. if x < 2^-27 (hx<0x3e400000 0), return 1 with inexact if x!=0. | ||
* 3. cos(x) is approximated by a polynomial of degree 14 on | ||
* [0,pi/4] | ||
* 4 14 | ||
* cos(x) ~ 1 - x*x/2 + C1*x + ... + C6*x | ||
* where the remez error is | ||
* | ||
* | 2 4 6 8 10 12 14 | -58 | ||
* |cos(x)-(1-.5*x +C1*x +C2*x +C3*x +C4*x +C5*x +C6*x )| <= 2 | ||
* | | | ||
* | ||
* 4 6 8 10 12 14 | ||
* 4. let r = C1*x +C2*x +C3*x +C4*x +C5*x +C6*x , then | ||
* cos(x) ~ 1 - x*x/2 + r | ||
* since cos(x+y) ~ cos(x) - sin(x)*y | ||
* ~ cos(x) - x*y, | ||
* a correction term is necessary in cos(x) and hence | ||
* cos(x+y) = 1 - (x*x/2 - (r - x*y)) | ||
* For better accuracy, rearrange to | ||
* cos(x+y) ~ w + (tmp + (r-x*y)) | ||
* where w = 1 - x*x/2 and tmp is a tiny correction term | ||
* (1 - x*x/2 == w + tmp exactly in infinite precision). | ||
* The exactness of w + tmp in infinite precision depends on w | ||
* and tmp having the same precision as x. If they have extra | ||
* precision due to compiler bugs, then the extra precision is | ||
* only good provided it is retained in all terms of the final | ||
* expression for cos(). Retention happens in all cases tested | ||
* under FreeBSD, so don't pessimize things by forcibly clipping | ||
* any extra precision in w. | ||
*/ | ||
@unsafe | ||
provide let cos = (x: WasmF64, y: WasmF64) => { | ||
use WasmF64.{ (+), (-), (*) } | ||
let c1 = 4.16666666666666019037e-02W /* 0x3FA55555, 0x5555554C */ | ||
let c2 = -1.38888888888741095749e-03W /* 0xBF56C16C, 0x16C15177 */ | ||
let c3 = 2.48015872894767294178e-05W /* 0x3EFA01A0, 0x19CB1590 */ | ||
let c4 = -2.75573143513906633035e-07W /* 0xBE927E4F, 0x809C52AD */ | ||
let c5 = 2.08757232129817482790e-09W /* 0x3E21EE9E, 0xBDB4B1C4 */ | ||
let c6 = -1.13596475577881948265e-11W /* 0xBDA8FAE9, 0xBE8838D4 */ | ||
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let z = x * x | ||
let w = z * z | ||
let r = z * (c1 + z * (c2 + z * c3)) + w * w * (c4 + z * (c5 + z * c6)) | ||
let hz = 0.5W * z | ||
let w = 1.0W - hz | ||
w + (1.0W - w - hz + (z * r - x * y)) | ||
} |
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--- | ||
title: Cosine | ||
--- | ||
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## Values | ||
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Functions and constants included in the Cosine module. | ||
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### Cosine.**cos** | ||
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```grain | ||
cos : (x: WasmF64, y: WasmF64) => WasmF64 | ||
``` | ||
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