e_sqrtf.c revision 2117
1115829Sfanf/* e_sqrtf.c -- float version of e_sqrt.c. 2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. 3 */ 4 5/* 6 * ==================================================== 7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 8 * 9 * Developed at SunPro, a Sun Microsystems, Inc. business. 10 * Permission to use, copy, modify, and distribute this 11 * software is freely granted, provided that this notice 12 * is preserved. 13 * ==================================================== 14 */ 15 16#ifndef lint 17static char rcsid[] = "$Id: e_sqrtf.c,v 1.2 1994/08/18 23:06:07 jtc Exp $"; 18#endif 19 20#include "math.h" 21#include "math_private.h" 22 23#ifdef __STDC__ 24static const float one = 1.0, tiny=1.0e-30; 25#else 26static float one = 1.0, tiny=1.0e-30; 27#endif 28 29#ifdef __STDC__ 30 float __ieee754_sqrtf(float x) 31#else 32 float __ieee754_sqrtf(x) 33 float x; 34#endif 35{ 36 float z; 37 int32_t sign = (int)0x80000000; 38 int32_t ix,s,q,m,t,i; 39 u_int32_t r; 40 41 GET_FLOAT_WORD(ix,x); 42 43 /* take care of Inf and NaN */ 44 if((ix&0x7f800000)==0x7f800000) { 45 return x*x+x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf 46 sqrt(-inf)=sNaN */ 47 } 48 /* take care of zero */ 49 if(ix<=0) { 50 if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */ 51 else if(ix<0) 52 return (x-x)/(x-x); /* sqrt(-ve) = sNaN */ 53 } 54 /* normalize x */ 55 m = (ix>>23); 56 if(m==0) { /* subnormal x */ 57 for(i=0;(ix&0x00800000)==0;i++) ix<<=1; 58 m -= i-1; 59 } 60 m -= 127; /* unbias exponent */ 61 ix = (ix&0x007fffff)|0x00800000; 62 if(m&1) /* odd m, double x to make it even */ 63 ix += ix; 64 m >>= 1; /* m = [m/2] */ 65 66 /* generate sqrt(x) bit by bit */ 67 ix += ix; 68 q = s = 0; /* q = sqrt(x) */ 69 r = 0x01000000; /* r = moving bit from right to left */ 70 71 while(r!=0) { 72 t = s+r; 73 if(t<=ix) { 74 s = t+r; 75 ix -= t; 76 q += r; 77 } 78 ix += ix; 79 r>>=1; 80 } 81 82 /* use floating add to find out rounding direction */ 83 if(ix!=0) { 84 z = one-tiny; /* trigger inexact flag */ 85 if (z>=one) { 86 z = one+tiny; 87 if (z>one) 88 q += 2; 89 else 90 q += (q&1); 91 } 92 } 93 ix = (q>>1)+0x3f000000; 94 ix += (m <<23); 95 SET_FLOAT_WORD(z,ix); 96 return z; 97} 98