1 2 /* 3 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. Oracle designates this 9 * particular file as subject to the "Classpath" exception as provided 10 * by Oracle in the LICENSE file that accompanied this code. 11 * 12 * This code is distributed in the hope that it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 * version 2 for more details (a copy is included in the LICENSE file that 16 * accompanied this code). 17 * 18 * You should have received a copy of the GNU General Public License version 19 * 2 along with this work; if not, write to the Free Software Foundation, 20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 21 * 22 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 23 * or visit www.oracle.com if you need additional information or have any 24 * questions. 25 */ 26 27 /* 28 * __kernel_rem_pio2(x,y,e0,nx,prec,ipio2) 29 * double x[],y[]; int e0,nx,prec; int ipio2[]; 30 * 31 * __kernel_rem_pio2 return the last three digits of N with 32 * y = x - N*pi/2 33 * so that |y| < pi/2. 34 * 35 * The method is to compute the integer (mod 8) and fraction parts of 36 * (2/pi)*x without doing the full multiplication. In general we 37 * skip the part of the product that are known to be a huge integer ( 38 * more accurately, = 0 mod 8 ). Thus the number of operations are 39 * independent of the exponent of the input. 40 * 41 * (2/pi) is represented by an array of 24-bit integers in ipio2[]. 42 * 43 * Input parameters: 44 * x[] The input value (must be positive) is broken into nx 45 * pieces of 24-bit integers in double precision format. 46 * x[i] will be the i-th 24 bit of x. The scaled exponent 47 * of x[0] is given in input parameter e0 (i.e., x[0]*2^e0 48 * match x's up to 24 bits. 49 * 50 * Example of breaking a double positive z into x[0]+x[1]+x[2]: 51 * e0 = ilogb(z)-23 52 * z = scalbn(z,-e0) 53 * for i = 0,1,2 54 * x[i] = floor(z) 55 * z = (z-x[i])*2**24 56 * 57 * 58 * y[] output result in an array of double precision numbers. 59 * The dimension of y[] is: 60 * 24-bit precision 1 61 * 53-bit precision 2 62 * 64-bit precision 2 63 * 113-bit precision 3 64 * The actual value is the sum of them. Thus for 113-bit 65 * precison, one may have to do something like: 66 * 67 * long double t,w,r_head, r_tail; 68 * t = (long double)y[2] + (long double)y[1]; 69 * w = (long double)y[0]; 70 * r_head = t+w; 71 * r_tail = w - (r_head - t); 72 * 73 * e0 The exponent of x[0] 74 * 75 * nx dimension of x[] 76 * 77 * prec an integer indicating the precision: 78 * 0 24 bits (single) 79 * 1 53 bits (double) 80 * 2 64 bits (extended) 81 * 3 113 bits (quad) 82 * 83 * ipio2[] 84 * integer array, contains the (24*i)-th to (24*i+23)-th 85 * bit of 2/pi after binary point. The corresponding 86 * floating value is 87 * 88 * ipio2[i] * 2^(-24(i+1)). 89 * 90 * External function: 91 * double scalbn(), floor(); 92 * 93 * 94 * Here is the description of some local variables: 95 * 96 * jk jk+1 is the initial number of terms of ipio2[] needed 97 * in the computation. The recommended value is 2,3,4, 98 * 6 for single, double, extended,and quad. 99 * 100 * jz local integer variable indicating the number of 101 * terms of ipio2[] used. 102 * 103 * jx nx - 1 104 * 105 * jv index for pointing to the suitable ipio2[] for the 106 * computation. In general, we want 107 * ( 2^e0*x[0] * ipio2[jv-1]*2^(-24jv) )/8 108 * is an integer. Thus 109 * e0-3-24*jv >= 0 or (e0-3)/24 >= jv 110 * Hence jv = max(0,(e0-3)/24). 111 * 112 * jp jp+1 is the number of terms in PIo2[] needed, jp = jk. 113 * 114 * q[] double array with integral value, representing the 115 * 24-bits chunk of the product of x and 2/pi. 116 * 117 * q0 the corresponding exponent of q[0]. Note that the 118 * exponent for q[i] would be q0-24*i. 119 * 120 * PIo2[] double precision array, obtained by cutting pi/2 121 * into 24 bits chunks. 122 * 123 * f[] ipio2[] in floating point 124 * 125 * iq[] integer array by breaking up q[] in 24-bits chunk. 126 * 127 * fq[] final product of x*(2/pi) in fq[0],..,fq[jk] 128 * 129 * ih integer. If >0 it indicates q[] is >= 0.5, hence 130 * it also indicates the *sign* of the result. 131 * 132 */ 133 134 135 /* 136 * Constants: 137 * The hexadecimal values are the intended ones for the following 138 * constants. The decimal values may be used, provided that the 139 * compiler will convert from decimal to binary accurately enough 140 * to produce the hexadecimal values shown. 141 */ 142 143 #include "fdlibm.h" 144 145 #ifdef __STDC__ 146 static const int init_jk[] = {2,3,4,6}; /* initial value for jk */ 147 #else 148 static int init_jk[] = {2,3,4,6}; 149 #endif 150 151 #ifdef __STDC__ 152 static const double PIo2[] = { 153 #else 154 static double PIo2[] = { 155 #endif 156 1.57079625129699707031e+00, /* 0x3FF921FB, 0x40000000 */ 157 7.54978941586159635335e-08, /* 0x3E74442D, 0x00000000 */ 158 5.39030252995776476554e-15, /* 0x3CF84698, 0x80000000 */ 159 3.28200341580791294123e-22, /* 0x3B78CC51, 0x60000000 */ 160 1.27065575308067607349e-29, /* 0x39F01B83, 0x80000000 */ 161 1.22933308981111328932e-36, /* 0x387A2520, 0x40000000 */ 162 2.73370053816464559624e-44, /* 0x36E38222, 0x80000000 */ 163 2.16741683877804819444e-51, /* 0x3569F31D, 0x00000000 */ 164 }; 165 166 #ifdef __STDC__ 167 static const double 168 #else 169 static double 170 #endif 171 zero = 0.0, 172 one = 1.0, 173 two24 = 1.67772160000000000000e+07, /* 0x41700000, 0x00000000 */ 174 twon24 = 5.96046447753906250000e-08; /* 0x3E700000, 0x00000000 */ 175 176 #ifdef __STDC__ 177 int __kernel_rem_pio2(double *x, double *y, int e0, int nx, int prec, const int *ipio2) 178 #else 179 int __kernel_rem_pio2(x,y,e0,nx,prec,ipio2) 180 double x[], y[]; int e0,nx,prec; int ipio2[]; 181 #endif 182 { 183 int jz,jx,jv,jp,jk,carry,n,iq[20],i,j,k,m,q0,ih; 184 double z,fw,f[20],fq[20],q[20]; 185 186 /* initialize jk*/ 187 jk = init_jk[prec]; 188 jp = jk; 189 190 /* determine jx,jv,q0, note that 3>q0 */ 191 jx = nx-1; 192 jv = (e0-3)/24; if(jv<0) jv=0; 193 q0 = e0-24*(jv+1); 194 195 /* set up f[0] to f[jx+jk] where f[jx+jk] = ipio2[jv+jk] */ 196 j = jv-jx; m = jx+jk; 197 for(i=0;i<=m;i++,j++) f[i] = (j<0)? zero : (double) ipio2[j]; 198 199 /* compute q[0],q[1],...q[jk] */ 200 for (i=0;i<=jk;i++) { 201 for(j=0,fw=0.0;j<=jx;j++) fw += x[j]*f[jx+i-j]; q[i] = fw; 202 } 203 204 jz = jk; 205 recompute: 206 /* distill q[] into iq[] reversingly */ 207 for(i=0,j=jz,z=q[jz];j>0;i++,j--) { 208 fw = (double)((int)(twon24* z)); 209 iq[i] = (int)(z-two24*fw); 210 z = q[j-1]+fw; 211 } 212 213 /* compute n */ 214 z = scalbn(z,q0); /* actual value of z */ 215 z -= 8.0*floor(z*0.125); /* trim off integer >= 8 */ 216 n = (int) z; 217 z -= (double)n; 218 ih = 0; 219 if(q0>0) { /* need iq[jz-1] to determine n */ 220 i = (iq[jz-1]>>(24-q0)); n += i; 221 iq[jz-1] -= i<<(24-q0); 222 ih = iq[jz-1]>>(23-q0); 223 } 224 else if(q0==0) ih = iq[jz-1]>>23; 225 else if(z>=0.5) ih=2; 226 227 if(ih>0) { /* q > 0.5 */ 228 n += 1; carry = 0; 229 for(i=0;i<jz ;i++) { /* compute 1-q */ 230 j = iq[i]; 231 if(carry==0) { 232 if(j!=0) { 233 carry = 1; iq[i] = 0x1000000- j; 234 } 235 } else iq[i] = 0xffffff - j; 236 } 237 if(q0>0) { /* rare case: chance is 1 in 12 */ 238 switch(q0) { 239 case 1: 240 iq[jz-1] &= 0x7fffff; break; 241 case 2: 242 iq[jz-1] &= 0x3fffff; break; 243 } 244 } 245 if(ih==2) { 246 z = one - z; 247 if(carry!=0) z -= scalbn(one,q0); 248 } 249 } 250 251 /* check if recomputation is needed */ 252 if(z==zero) { 253 j = 0; 254 for (i=jz-1;i>=jk;i--) j |= iq[i]; 255 if(j==0) { /* need recomputation */ 256 for(k=1;iq[jk-k]==0;k++); /* k = no. of terms needed */ 257 258 for(i=jz+1;i<=jz+k;i++) { /* add q[jz+1] to q[jz+k] */ 259 f[jx+i] = (double) ipio2[jv+i]; 260 for(j=0,fw=0.0;j<=jx;j++) fw += x[j]*f[jx+i-j]; 261 q[i] = fw; 262 } 263 jz += k; 264 goto recompute; 265 } 266 } 267 268 /* chop off zero terms */ 269 if(z==0.0) { 270 jz -= 1; q0 -= 24; 271 while(iq[jz]==0) { jz--; q0-=24;} 272 } else { /* break z into 24-bit if necessary */ 273 z = scalbn(z,-q0); 274 if(z>=two24) { 275 fw = (double)((int)(twon24*z)); 276 iq[jz] = (int)(z-two24*fw); 277 jz += 1; q0 += 24; 278 iq[jz] = (int) fw; 279 } else iq[jz] = (int) z ; 280 } 281 282 /* convert integer "bit" chunk to floating-point value */ 283 fw = scalbn(one,q0); 284 for(i=jz;i>=0;i--) { 285 q[i] = fw*(double)iq[i]; fw*=twon24; 286 } 287 288 /* compute PIo2[0,...,jp]*q[jz,...,0] */ 289 for(i=jz;i>=0;i--) { 290 for(fw=0.0,k=0;k<=jp&&k<=jz-i;k++) fw += PIo2[k]*q[i+k]; 291 fq[jz-i] = fw; 292 } 293 294 /* compress fq[] into y[] */ 295 switch(prec) { 296 case 0: 297 fw = 0.0; 298 for (i=jz;i>=0;i--) fw += fq[i]; 299 y[0] = (ih==0)? fw: -fw; 300 break; 301 case 1: 302 case 2: 303 fw = 0.0; 304 for (i=jz;i>=0;i--) fw += fq[i]; 305 y[0] = (ih==0)? fw: -fw; 306 fw = fq[0]-fw; 307 for (i=1;i<=jz;i++) fw += fq[i]; 308 y[1] = (ih==0)? fw: -fw; 309 break; 310 case 3: /* painful */ 311 for (i=jz;i>0;i--) { 312 fw = fq[i-1]+fq[i]; 313 fq[i] += fq[i-1]-fw; 314 fq[i-1] = fw; 315 } 316 for (i=jz;i>1;i--) { 317 fw = fq[i-1]+fq[i]; 318 fq[i] += fq[i-1]-fw; 319 fq[i-1] = fw; 320 } 321 for (fw=0.0,i=jz;i>=2;i--) fw += fq[i]; 322 if(ih==0) { 323 y[0] = fq[0]; y[1] = fq[1]; y[2] = fw; 324 } else { 325 y[0] = -fq[0]; y[1] = -fq[1]; y[2] = -fw; 326 } 327 } 328 return n&7; 329 }