diff options
Diffstat (limited to 'sysdeps/ieee754/dbl-64/halfulp.c')
| -rw-r--r-- | sysdeps/ieee754/dbl-64/halfulp.c | 124 |
1 files changed, 124 insertions, 0 deletions
diff --git a/sysdeps/ieee754/dbl-64/halfulp.c b/sysdeps/ieee754/dbl-64/halfulp.c new file mode 100644 index 0000000000..7901ec4e36 --- /dev/null +++ b/sysdeps/ieee754/dbl-64/halfulp.c @@ -0,0 +1,124 @@ + +/* + * IBM Accurate Mathematical Library + * Copyright (c) International Business Machines Corp., 2001 + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + */ +/************************************************************************/ +/* */ +/* MODULE_NAME:halfulp.c */ +/* */ +/* FUNCTIONS:halfulp */ +/* FILES NEEDED: mydefs.h dla.h endian.h */ +/* uroot.c */ +/* */ +/*Routine halfulp(double x, double y) computes x^y where result does */ +/*not need rounding. If the result is closer to 0 than can be */ +/*represented it returns 0. */ +/* In the following cases the function does not compute anything */ +/*and returns a negative number: */ +/*1. if the result needs rounding, */ +/*2. if y is outside the interval [0, 2^20-1], */ +/*3. if x can be represented by x=2**n for some integer n. */ +/************************************************************************/ + +#include "endian.h" +#include "mydefs.h" +#include "dla.h" + +double usqrt(double x); + +int4 tab54[32] = { + 262143, 11585, 1782, 511, 210, 107, 63, 42, + 30, 22, 17, 14, 12, 10, 9, 7, + 7, 6, 5, 5, 5, 4, 4, 4, + 3, 3, 3, 3, 3, 3, 3, 3 }; + + +double halfulp(double x, double y) +{ + mynumber v; + double z,u,uu,j1,j2,j3,j4,j5; + int4 k,l,m,n; + if (y <= 0) { /*if power is negative or zero */ + v.x = y; + if (v.i[LOW_HALF] != 0) return -10.0; + v.x = x; + if (v.i[LOW_HALF] != 0) return -10.0; + if ((v.i[HIGH_HALF]&0x000fffff) != 0) return -10; /* if x =2 ^ n */ + k = ((v.i[HIGH_HALF]&0x7fffffff)>>20)-1023; /* find this n */ + z = (double) k; + return (z*y == -1075.0)?0: -10.0; + } + /* if y > 0 */ + v.x = y; + if (v.i[LOW_HALF] != 0) return -10.0; + + v.x=x; + /* case where x = 2**n for some integer n */ + if (((v.i[HIGH_HALF]&0x000fffff)|v.i[LOW_HALF]) == 0) { + k=(v.i[HIGH_HALF]>>20)-1023; + return (((double) k)*y == -1075.0)?0:-10.0; + } + + v.x = y; + k = v.i[HIGH_HALF]; + m = k<<12; + l = 0; + while (m) + {m = m<<1; l++; } + n = (k&0x000fffff)|0x00100000; + n = n>>(20-l); /* n is the odd integer of y */ + k = ((k>>20) -1023)-l; /* y = n*2**k */ + if (k>5) return -10.0; + if (k>0) for (;k>0;k--) n *= 2; + if (n > 34) return -10.0; + k = -k; + if (k>5) return -10.0; + + /* now treat x */ + while (k>0) { + z = usqrt(x); + EMULV(z,z,u,uu,j1,j2,j3,j4,j5); + if (((u-x)+uu) != 0) break; + x = z; + k--; + } + if (k) return -10.0; + + /* it is impossible that n == 2, so the mantissa of x must be short */ + + v.x = x; + if (v.i[LOW_HALF]) return -10.0; + k = v.i[HIGH_HALF]; + m = k<<12; + l = 0; + while (m) {m = m<<1; l++; } + m = (k&0x000fffff)|0x00100000; + m = m>>(20-l); /* m is the odd integer of x */ + + /* now check whether the length of m**n is at most 54 bits */ + + if (m > tab54[n-3]) return -10.0; + + /* yes, it is - now compute x**n by simple multiplications */ + + u = x; + for (k=1;k<n;k++) u = u*x; + return u; +} + + |