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c3c/lib/std/math/math_nolibc/rempi.c3
Christoffer Lerno 25bccf4883 New faults and syntax (#2034)
- Remove `[?]` syntax.
- Change `int!` to `int?` syntax.
- New `fault` declarations.
- Enum associated values can reference the calling enum.
2025-03-10 00:11:35 +01:00

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module std::math::nolibc @if(env::NO_LIBC || $feature(C3_MATH));
import std::math;
/* origin: FreeBSD /usr/src/lib/msun/src/e_rem_pio2f.c */
/*
* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
* Debugged and optimized by Bruce D. Evans.
*/
/*
* ====================================================
* 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.
* ====================================================
*/
/* __rem_pio2f(x,y)
*
* return the remainder of x rem pi/2 in *y
* use double precision for everything except passing x
* use __rem_pio2_large() for large x
*/
/*
* invpio2: 53 bits of 2/pi
* pio2_1: first 25 bits of pi/2
* pio2_1t: pi/2 - pio2_1
*/
fn int __rem_pio2f(float x, double *y)
{
const double PIO4 = 0x1.921fb6p-1;
const double INVPIO2 = 6.36619772367581382433e-01; /* 0x3FE45F30, 0x6DC9C883 */
const double PIO2_1 = 1.57079631090164184570e+00; /* 0x3FF921FB, 0x50000000 */
const double PIO2_1T = 1.58932547735281966916e-08; /* 0x3E5110b4, 0x611A6263 */
uint ux = bitcast(x, uint);
uint ix = ux & 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 f.
uint f = (uint)(((double)x * INVPIO2 + TOINT15) - TOINT15);
int n = (int)f;
*y = x - f * PIO2_1 - f * PIO2_1T;
/* Matters with directed rounding. */
if (*y < -PIO4) // likely false
{
n--;
f--;
*y = x - f * PIO2_1 - f * PIO2_1T;
}
else if (*y > PIO4) // likely false
{
n++;
f++;
*y = x - f * PIO2_1 - f * PIO2_1T;
}
return n;
}
if (ix >= 0x7f800000)
{
// x is inf or NaN
*y = x - (double)x;
return 0;
}
/* scale x into [2^23, 2^24-1] */
int sign = ux >> 31;
int e0 = (ix >> 23) - (0x7f + 23); /* e0 = ilogb(|x|)-23, positive */
ux = ix - e0 << 23;
double tx = bitcast(ux, float);
double ty @noinit;
int n = __rem_pio2_large(&tx,&ty, e0, 1, 0);
if (sign)
{
*y = (float)-ty;
return -n;
}
*y = (float)ty;
return n;
}
/* origin: FreeBSD /usr/src/lib/msun/src/k_rem_pio2.c */
/*
* ====================================================
* 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.
* ====================================================
*/
const int[*] INIT_JK = {3,4,4,6}; /* initial value for jk */
const int[*] IPIO2 = {
0xA2F983, 0x6E4E44, 0x1529FC, 0x2757D1, 0xF534DD, 0xC0DB62,
0x95993C, 0x439041, 0xFE5163, 0xABDEBB, 0xC561B7, 0x246E3A,
0x424DD2, 0xE00649, 0x2EEA09, 0xD1921C, 0xFE1DEB, 0x1CB129,
0xA73EE8, 0x8235F5, 0x2EBB44, 0x84E99C, 0x7026B4, 0x5F7E41,
0x3991D6, 0x398353, 0x39F49C, 0x845F8B, 0xBDF928, 0x3B1FF8,
0x97FFDE, 0x05980F, 0xEF2F11, 0x8B5A0A, 0x6D1F6D, 0x367ECF,
0x27CB09, 0xB74F46, 0x3F669E, 0x5FEA2D, 0x7527BA, 0xC7EBE5,
0xF17B3D, 0x0739F7, 0x8A5292, 0xEA6BFB, 0x5FB11F, 0x8D5D08,
0x560330, 0x46FC7B, 0x6BABF0, 0xCFBC20, 0x9AF436, 0x1DA9E3,
0x91615E, 0xE61B08, 0x659985, 0x5F14A0, 0x68408D, 0xFFD880,
0x4D7327, 0x310606, 0x1556CA, 0x73A8C9, 0x60E27B, 0xC08C6B, };
const double[*] PIO2 = {
1.57079625129699707031e+00, /* 0x3FF921FB, 0x40000000 */
7.54978941586159635335e-08, /* 0x3E74442D, 0x00000000 */
5.39030252995776476554e-15, /* 0x3CF84698, 0x80000000 */
3.28200341580791294123e-22, /* 0x3B78CC51, 0x60000000 */
1.27065575308067607349e-29, /* 0x39F01B83, 0x80000000 */
1.22933308981111328932e-36, /* 0x387A2520, 0x40000000 */
2.73370053816464559624e-44, /* 0x36E38222, 0x80000000 */
2.16741683877804819444e-51, /* 0x3569F31D, 0x00000000 */
};
fn int __rem_pio2_large(double* x, double* y, int e0, int nx, int prec)
{
double[20] f @noinit;
double[20] fq @noinit;
double[20] q @noinit;
int[20] iq @noinit;
double fw @noinit;
/* initialize jk*/
int jk = INIT_JK[prec];
int jp = jk;
/* determine jx,jv,q0, note that 3>q0 */
int jx = nx - 1;
int jv = (e0 - 3) / 24;
if (jv < 0) jv = 0;
int q0 = e0 - 24 * (jv + 1);
// set up f[0] to f[jx+jk] where f[jx+jk] = ipio2[jv+jk]
int j = jv - jx;
int m = jx + jk;
for (int i = 0; i <= m; i++, j++)
{
f[i] = j < 0 ? 0.0 : (double)IPIO2[j];
}
// compute q[0],q[1],...q[jk]
for (int i = 0; i <= jk; i++)
{
for (j = 0, fw = 0.0; j <= jx; j++) fw += x[j] * f[jx + i - j];
q[i] = fw;
}
int jz = jk;
double z @noinit;
int ih = 0;
int n @noinit;
while (1)
{
/* distill q[] into iq[] reversingly */
z = q[jz];
j = jz;
for (int i = 0; j > 0; i++, j--)
{
fw = (double)(int)(0x1p-24 * z);
iq[i] = (int)(z - 0x1p24 * fw);
z = q[j - 1] + fw;
}
// compute n
z = nolibc::_scalbn(z, q0); /* actual value of z */
z -= 8.0 * nolibc::_floor(z * 0.125); /* trim off integer >= 8 */
n = (int)z;
z -= (double)n;
switch
{
case q0 > 0:
// need iq[jz-1] to determine n
int i = iq[jz - 1] >> (24 - q0);
n += i;
iq[jz - 1] -= i << (24 - q0);
ih = iq[jz - 1] >> (23 - q0);
case q0 == 0:
ih = iq[jz - 1] >> 23;
case z >= 0.5:
ih = 2;
}
if (ih > 0)
{
/* q > 0.5 */
n += 1;
int carry = 0;
for (int i = 0; i < jz; i++)
{
/* compute 1-q */
j = iq[i];
if (carry == 0)
{
if (j != 0)
{
carry = 1;
iq[i] = 0x1000000 - j;
}
}
else
{
iq[i] = 0xffffff - j;
}
}
if (q0 > 0)
{
/* rare case: chance is 1 in 12 */
switch (q0)
{
case 1: iq[jz - 1] &= 0x7fffff;
case 2: iq[jz - 1] &= 0x3fffff;
}
}
if (ih == 2)
{
z = 1.0 - z;
if (carry != 0) z -= nolibc::_scalbn(1.0, q0);
}
}
// check if recomputation is needed
if (z == 0.0)
{
j = 0;
for (int i = jz - 1; i >= jk; i--) j |= iq[i];
if (j == 0)
{
/* need recomputation */
int k = 1;
for (; iq[jk - k] == 0; k++); /* k = no. of terms needed */
for (int i = jz + 1; i <= jz + k; i++)
{
/* add q[jz+1] to q[jz+k] */
f[jx + i] = (double)IPIO2[jv + i];
for (j = 0, fw = 0.0; j <= jx; j++) fw += x[j] * f[jx + i - j];
q[i] = fw;
}
jz += k;
continue;
}
}
break;
}
/* chop off zero terms */
if (z == 0.0)
{
jz -= 1;
q0 -= 24;
while (iq[jz] == 0)
{
jz--;
q0 -= 24;
}
}
else
{
/* break z into 24-bit if necessary */
z = _scalbn(z,-q0);
if (z >= 0x1p24)
{
fw = (double)(int)(0x1p-24 * z);
iq[jz] = (int)(z - 0x1p24 * fw);
jz += 1;
q0 += 24;
iq[jz] = (int)fw;
}
else
{
iq[jz] = (int)z;
}
}
/* convert integer "bit" chunk to floating-point value */
fw = nolibc::_scalbn(1.0 , q0);
for (int i = jz; i >= 0; i --)
{
q[i] = fw * (double)iq[i];
fw *= 0x1p-24;
}
/* compute PIO2[0,...,jp]*q[jz,...,0] */
for (int i = jz; i >= 0; i--)
{
for (fw = 0.0, int k = 0; k <= jp && k <= jz-i; k++) fw += PIO2[k] * q[i + k];
fq[jz - i] = fw;
}
/* compress fq[] into y[] */
switch (prec)
{
case 0:
fw = 0.0;
for (int i = jz; i >= 0; i--) fw += fq[i];
y[0] = ih == 0 ? fw : -fw;
case 1:
case 2:
fw = 0.0;
for (int i = jz; i >= 0; i--) fw += fq[i];
// TODO: drop excess precision here once double_t is used
fw = (double)fw;
y[0] = ih == 0 ? fw : -fw;
fw = fq[0]-fw;
for (int i = 1; i <= jz; i++) fw += fq[i];
y[1] = ih == 0 ? fw : -fw;
case 3: /* painful */
for (int i = jz; i > 0; i--)
{
fw = fq[i - 1] + fq[i];
fq[i] += fq[i - 1] - fw;
fq[i - 1] = fw;
}
for (int i = jz; i > 1; i--)
{
fw = fq[i-1] + fq[i];
fq[i] += fq[i - 1] - fw;
fq[i - 1] = fw;
}
for (fw = 0.0, int i = jz; i >= 2; i--) fw += fq[i];
if (ih == 0)
{
y[0] = fq[0];
y[1] = fq[1];
y[2] = fw;
}
else
{
y[0] = -fq[0];
y[1] = -fq[1];
y[2] = -fw;
}
}
return n & 7;
}
/* origin: FreeBSD /usr/src/lib/msun/src/e_rem_pio2.c */
/*
* ====================================================
* 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.
* ====================================================
*
* Optimized by Bruce D. Evans.
*/
/*
* invpio2: 53 bits of 2/pi
* pio2_1: first 33 bit of pi/2
* pio2_1t: pi/2 - pio2_1
* pio2_2: second 33 bit of pi/2
* pio2_2t: pi/2 - (pio2_1+pio2_2)
* pio2_3: third 33 bit of pi/2
* pio2_3t: pi/2 - (pio2_1+pio2_2+pio2_3)
*/
<* caller must handle the case when reduction is not needed: |x| ~<= pi/4 *>
fn int __rem_pio2(double x, double *y)
{
const double PIO4 = 0x1.921fb54442d18p-1;
const double INVPIO2 = 6.36619772367581382433e-01; /* 0x3FE45F30, 0x6DC9C883 */
const double PIO2_1 = 1.57079632673412561417e+00; /* 0x3FF921FB, 0x54400000 */
const double PIO2_1T = 6.07710050650619224932e-11; /* 0x3DD0B461, 0x1A626331 */
const double PIO2_2 = 6.07710050630396597660e-11; /* 0x3DD0B461, 0x1A600000 */
const double PIO2_2T = 2.02226624879595063154e-21; /* 0x3BA3198A, 0x2E037073 */
const double PIO2_3 = 2.02226624871116645580e-21; /* 0x3BA3198A, 0x2E000000 */
const double PIO2_3T = 8.47842766036889956997e-32; /* 0x397B839A, 0x252049C1 */
ulong u = bitcast(x, ulong);
int sign = (int)(u >> 63);
uint ix = (uint)(u >> 32 & 0x7fffffff);
switch
{
// |x| ~<= 5pi/4
case ix <= 0x400f6a7a:
// |x| ~= pi/2 or 2pi/2
if ((ix & 0xfffff) == 0x921fb)
{
// cancellation -- use medium case
break;
}
// |x| ~<= 3pi/4
if (ix <= 0x4002d97c)
{
if (!sign)
{
double z = x - PIO2_1; /* one round good to 85 bits */
y[0] = z - PIO2_1T;
y[1] = (z - y[0]) - PIO2_1T;
return 1;
}
double z = x + PIO2_1;
y[0] = z + PIO2_1T;
y[1] = (z - y[0]) + PIO2_1T;
return -1;
}
if (!sign)
{
double z = x - 2 * PIO2_1;
y[0] = z - 2 * PIO2_1T;
y[1] = (z - y[0]) - 2 * PIO2_1T;
return 2;
}
double z = x + 2 * PIO2_1;
y[0] = z + 2 * PIO2_1T;
y[1] = (z - y[0]) + 2 * PIO2_1T;
return -2;
// |x| ~<= 9pi/4
case ix <= 0x401c463b:
// |x| ~<= 7pi/4
if (ix <= 0x4015fdbc)
{
// |x| ~= 3pi/2
if (ix == 0x4012d97c) break; // Use medium
if (!sign)
{
double z = x - 3 * PIO2_1;
y[0] = z - 3 * PIO2_1T;
y[1] = (z - y[0]) - 3 * PIO2_1T;
return 3;
}
double z = x + 3 * PIO2_1;
y[0] = z + 3 * PIO2_1T;
y[1] = (z - y[0]) + 3 * PIO2_1T;
return -3;
}
// |x| ~= 4pi/2
if (ix == 0x401921fb) break; // Use medium
if (!sign)
{
double z = x - 4 * PIO2_1;
y[0] = z - 4 * PIO2_1T;
y[1] = (z - y[0]) - 4 * PIO2_1T;
return 4;
}
double z = x + 4*PIO2_1;
y[0] = z + 4 * PIO2_1T;
y[1] = (z - y[0]) + 4 * PIO2_1T;
return -4;
case ix < 0x413921fb:
break; // medium
case ix >= 0x7ff00000:
// x is inf or NaN
y[0] = y[1] = x - x;
return 0;
default:
// all other (large) arguments
// set z = scalbn(|x|,-ilogb(x)+23)
u = bitcast(x, ulong);
u &= ((ulong)-1) >> 12;
u |= (ulong)(0x3ff + 23) << 52;
double z = bitcast(u, double);
double[3] tx;
int i;
for (i = 0; i < 2; i++)
{
tx[i] = (double)(int)z;
z = (z - tx[i]) * 0x1p24;
}
tx[i] = z;
// skip zero terms, first term is non-zero
while (tx[i] == 0.0) i--;
double[2] ty;
int n = __rem_pio2_large(&tx, &ty, (int)(ix >> 20) - (0x3ff + 23), i + 1, 1);
if (sign)
{
y[0] = -ty[0];
y[1] = -ty[1];
return -n;
}
y[0] = ty[0];
y[1] = ty[1];
return n;
}
// |x| ~< 2^20*(pi/2), medium size
// rint(x/(pi/2))
double fnn = (double)x * INVPIO2 + TOINT15 - TOINT15;
int n = (int)fnn;
double r = x - fnn * PIO2_1;
double w = fnn * PIO2_1T; // 1st round, good to 85 bits
// Matters with directed rounding.
if (r - w < -PIO4) /*@unlikely*/
{
n--;
fnn--;
r = x - fnn * PIO2_1;
w = fnn * PIO2_1T;
}
else if (r - w > PIO4) /*@unlikely*/
{
n++;
fnn++;
r = x - fnn * PIO2_1;
w = fnn * PIO2_1T;
}
y[0] = r - w;
u = bitcast(y[0], ulong);
int ey = (int)(u >> 52 & 0x7ff);
int ex = (int)(ix >> 20);
if (ex - ey > 16)
{
// 2nd round, good to 118 bits
double t = r;
w = fnn * PIO2_2;
r = t - w;
w = fnn * PIO2_2T - ((t - r) - w);
y[0] = r - w;
u = bitcast(y[0], ulong);
ey = (int)(u >> 52 & 0x7ff);
if (ex - ey > 49)
{
// 3rd round, good to 151 bits, covers all cases
t = r;
w = fnn * PIO2_3;
r = t - w;
w = fnn * PIO2_3T - ((t - r) - w);
y[0] = r - w;
}
}
y[1] = (r - y[0]) - w;
return n;
}