e_rem_pio2l.h revision 176356
1 2/* @(#)e_rem_pio2.c 1.4 95/01/18 */ 3/* 4 * ==================================================== 5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 6 * 7 * Developed at SunSoft, a Sun Microsystems, Inc. business. 8 * Permission to use, copy, modify, and distribute this 9 * software is freely granted, provided that this notice 10 * is preserved. 11 * ==================================================== 12 * 13 */ 14 15#ifndef lint 16static char rcsid[] = "$FreeBSD: head/lib/msun/src/e_rem_pio2.c 176356 2008-02-17 07:31:59Z das $"; 17#endif 18 19/* __ieee754_rem_pio2(x,y) 20 * 21 * return the remainder of x rem pi/2 in y[0]+y[1] 22 * use __kernel_rem_pio2() 23 */ 24 25#include "math.h" 26#include "math_private.h" 27 28static const int32_t npio2_hw[] = { 290x3FF921FB, 0x400921FB, 0x4012D97C, 0x401921FB, 0x401F6A7A, 0x4022D97C, 300x4025FDBB, 0x402921FB, 0x402C463A, 0x402F6A7A, 0x4031475C, 0x4032D97C, 310x40346B9C, 0x4035FDBB, 0x40378FDB, 0x403921FB, 0x403AB41B, 0x403C463A, 320x403DD85A, 0x403F6A7A, 0x40407E4C, 0x4041475C, 0x4042106C, 0x4042D97C, 330x4043A28C, 0x40446B9C, 0x404534AC, 0x4045FDBB, 0x4046C6CB, 0x40478FDB, 340x404858EB, 0x404921FB, 35}; 36 37/* 38 * invpio2: 53 bits of 2/pi 39 * pio2_1: first 33 bit of pi/2 40 * pio2_1t: pi/2 - pio2_1 41 * pio2_2: second 33 bit of pi/2 42 * pio2_2t: pi/2 - (pio2_1+pio2_2) 43 * pio2_3: third 33 bit of pi/2 44 * pio2_3t: pi/2 - (pio2_1+pio2_2+pio2_3) 45 */ 46 47static const double 48zero = 0.00000000000000000000e+00, /* 0x00000000, 0x00000000 */ 49half = 5.00000000000000000000e-01, /* 0x3FE00000, 0x00000000 */ 50two24 = 1.67772160000000000000e+07, /* 0x41700000, 0x00000000 */ 51invpio2 = 6.36619772367581382433e-01, /* 0x3FE45F30, 0x6DC9C883 */ 52pio2_1 = 1.57079632673412561417e+00, /* 0x3FF921FB, 0x54400000 */ 53pio2_1t = 6.07710050650619224932e-11, /* 0x3DD0B461, 0x1A626331 */ 54pio2_2 = 6.07710050630396597660e-11, /* 0x3DD0B461, 0x1A600000 */ 55pio2_2t = 2.02226624879595063154e-21, /* 0x3BA3198A, 0x2E037073 */ 56pio2_3 = 2.02226624871116645580e-21, /* 0x3BA3198A, 0x2E000000 */ 57pio2_3t = 8.47842766036889956997e-32; /* 0x397B839A, 0x252049C1 */ 58 59 int32_t __ieee754_rem_pio2(double x, double *y) 60{ 61 double z,w,t,r,fn; 62 double tx[3]; 63 int32_t e0,i,j,nx,n,ix,hx; 64 u_int32_t low; 65 66 GET_HIGH_WORD(hx,x); /* high word of x */ 67 ix = hx&0x7fffffff; 68 if(ix<=0x3fe921fb) /* |x| ~<= pi/4 , no need for reduction */ 69 {y[0] = x; y[1] = 0; return 0;} 70 if(ix<0x4002d97c) { /* |x| < 3pi/4, special case with n=+-1 */ 71 if(hx>0) { 72 z = x - pio2_1; 73 if(ix!=0x3ff921fb) { /* 33+53 bit pi is good enough */ 74 y[0] = z - pio2_1t; 75 y[1] = (z-y[0])-pio2_1t; 76 } else { /* near pi/2, use 33+33+53 bit pi */ 77 z -= pio2_2; 78 y[0] = z - pio2_2t; 79 y[1] = (z-y[0])-pio2_2t; 80 } 81 return 1; 82 } else { /* negative x */ 83 z = x + pio2_1; 84 if(ix!=0x3ff921fb) { /* 33+53 bit pi is good enough */ 85 y[0] = z + pio2_1t; 86 y[1] = (z-y[0])+pio2_1t; 87 } else { /* near pi/2, use 33+33+53 bit pi */ 88 z += pio2_2; 89 y[0] = z + pio2_2t; 90 y[1] = (z-y[0])+pio2_2t; 91 } 92 return -1; 93 } 94 } 95 if(ix<=0x413921fb) { /* |x| ~<= 2^19*(pi/2), medium size */ 96 t = fabs(x); 97 n = (int32_t) (t*invpio2+half); 98 fn = (double)n; 99 r = t-fn*pio2_1; 100 w = fn*pio2_1t; /* 1st round good to 85 bit */ 101 if(n<32&&ix!=npio2_hw[n-1]) { 102 y[0] = r-w; /* quick check no cancellation */ 103 } else { 104 u_int32_t high; 105 j = ix>>20; 106 y[0] = r-w; 107 GET_HIGH_WORD(high,y[0]); 108 i = j-((high>>20)&0x7ff); 109 if(i>16) { /* 2nd iteration needed, good to 118 */ 110 t = r; 111 w = fn*pio2_2; 112 r = t-w; 113 w = fn*pio2_2t-((t-r)-w); 114 y[0] = r-w; 115 GET_HIGH_WORD(high,y[0]); 116 i = j-((high>>20)&0x7ff); 117 if(i>49) { /* 3rd iteration need, 151 bits acc */ 118 t = r; /* will cover all possible cases */ 119 w = fn*pio2_3; 120 r = t-w; 121 w = fn*pio2_3t-((t-r)-w); 122 y[0] = r-w; 123 } 124 } 125 } 126 y[1] = (r-y[0])-w; 127 if(hx<0) {y[0] = -y[0]; y[1] = -y[1]; return -n;} 128 else return n; 129 } 130 /* 131 * all other (large) arguments 132 */ 133 if(ix>=0x7ff00000) { /* x is inf or NaN */ 134 y[0]=y[1]=x-x; return 0; 135 } 136 /* set z = scalbn(|x|,ilogb(x)-23) */ 137 GET_LOW_WORD(low,x); 138 SET_LOW_WORD(z,low); 139 e0 = (ix>>20)-1046; /* e0 = ilogb(z)-23; */ 140 SET_HIGH_WORD(z, ix - ((int32_t)(e0<<20))); 141 for(i=0;i<2;i++) { 142 tx[i] = (double)((int32_t)(z)); 143 z = (z-tx[i])*two24; 144 } 145 tx[2] = z; 146 nx = 3; 147 while(tx[nx-1]==zero) nx--; /* skip zero term */ 148 n = __kernel_rem_pio2(tx,y,e0,nx,2); 149 if(hx<0) {y[0] = -y[0]; y[1] = -y[1]; return -n;} 150 return n; 151} 152