141 lines
4.0 KiB
C
141 lines
4.0 KiB
C
/* From: @(#)e_rem_pio2.c 1.4 95/01/18 */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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* Copyright (c) 2008 Steven G. Kargl, David Schultz, Bruce D. Evans.
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*
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* Developed at SunSoft, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*
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* Optimized by Bruce D. Evans.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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/* ld128 version of __ieee754_rem_pio2l(x,y)
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*
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* return the remainder of x rem pi/2 in y[0]+y[1]
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* use __kernel_rem_pio2()
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*/
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#include <float.h>
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#include "math.h"
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#include "math_private.h"
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#include "fpmath.h"
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#define BIAS (LDBL_MAX_EXP - 1)
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/*
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* XXX need to verify that nonzero integer multiples of pi/2 within the
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* range get no closer to a long double than 2**-140, or that
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* ilogb(x) + ilogb(min_delta) < 45 - -140.
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*/
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/*
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* invpio2: 113 bits of 2/pi
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* pio2_1: first 68 bits of pi/2
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* pio2_1t: pi/2 - pio2_1
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* pio2_2: second 68 bits of pi/2
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* pio2_2t: pi/2 - (pio2_1+pio2_2)
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* pio2_3: third 68 bits of pi/2
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* pio2_3t: pi/2 - (pio2_1+pio2_2+pio2_3)
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*/
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static const double
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zero = 0.00000000000000000000e+00, /* 0x00000000, 0x00000000 */
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two24 = 1.67772160000000000000e+07; /* 0x41700000, 0x00000000 */
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static const long double
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invpio2 = 6.3661977236758134307553505349005747e-01L, /* 0x145f306dc9c882a53f84eafa3ea6a.0p-113 */
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pio2_1 = 1.5707963267948966192292994253909555e+00L, /* 0x1921fb54442d18469800000000000.0p-112 */
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pio2_1t = 2.0222662487959507323996846200947577e-21L, /* 0x13198a2e03707344a4093822299f3.0p-181 */
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pio2_2 = 2.0222662487959507323994779168837751e-21L, /* 0x13198a2e03707344a400000000000.0p-181 */
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pio2_2t = 2.0670321098263988236496903051604844e-43L, /* 0x127044533e63a0105df531d89cd91.0p-254 */
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pio2_3 = 2.0670321098263988236499468110329591e-43L, /* 0x127044533e63a0105e00000000000.0p-254 */
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pio2_3t = -2.5650587247459238361625433492959285e-65L; /* -0x159c4ec64ddaeb5f78671cbfb2210.0p-327 */
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static inline __always_inline int
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__ieee754_rem_pio2l(long double x, long double *y)
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{
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union IEEEl2bits u,u1;
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long double z,w,t,r,fn;
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double tx[5],ty[3];
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int64_t n;
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int e0,ex,i,j,nx;
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int16_t expsign;
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u.e = x;
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expsign = u.xbits.expsign;
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ex = expsign & 0x7fff;
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if (ex < BIAS + 45 || ex == BIAS + 45 &&
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u.bits.manh < 0x921fb54442d1LL) {
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/* |x| ~< 2^45*(pi/2), medium size */
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/* Use a specialized rint() to get fn. Assume round-to-nearest. */
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fn = x*invpio2+0x1.8p112;
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fn = fn-0x1.8p112;
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#ifdef HAVE_EFFICIENT_I64RINT
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n = i64rint(fn);
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#else
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n = fn;
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#endif
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r = x-fn*pio2_1;
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w = fn*pio2_1t; /* 1st round good to 180 bit */
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{
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union IEEEl2bits u2;
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int ex1;
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j = ex;
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y[0] = r-w;
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u2.e = y[0];
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ex1 = u2.xbits.expsign & 0x7fff;
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i = j-ex1;
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if(i>51) { /* 2nd iteration needed, good to 248 */
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t = r;
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w = fn*pio2_2;
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r = t-w;
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w = fn*pio2_2t-((t-r)-w);
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y[0] = r-w;
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u2.e = y[0];
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ex1 = u2.xbits.expsign & 0x7fff;
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i = j-ex1;
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if(i>119) { /* 3rd iteration need, 316 bits acc */
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t = r; /* will cover all possible cases */
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w = fn*pio2_3;
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r = t-w;
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w = fn*pio2_3t-((t-r)-w);
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y[0] = r-w;
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}
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}
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}
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y[1] = (r-y[0])-w;
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return n;
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}
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/*
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* all other (large) arguments
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*/
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if(ex==0x7fff) { /* x is inf or NaN */
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y[0]=y[1]=x-x; return 0;
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}
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/* set z = scalbn(|x|,ilogb(x)-23) */
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u1.e = x;
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e0 = ex - BIAS - 23; /* e0 = ilogb(|x|)-23; */
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u1.xbits.expsign = ex - e0;
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z = u1.e;
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for(i=0;i<4;i++) {
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tx[i] = (double)((int32_t)(z));
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z = (z-tx[i])*two24;
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}
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tx[4] = z;
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nx = 5;
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while(tx[nx-1]==zero) nx--; /* skip zero term */
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n = __kernel_rem_pio2(tx,ty,e0,nx,3);
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t = (long double)ty[2] + ty[1];
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r = t + ty[0];
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w = ty[0] - (r - t);
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if(expsign<0) {y[0] = -r; y[1] = -w; return -n;}
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y[0] = r; y[1] = w; return n;
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}
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