e_sqrtf.c revision 97409
1/* 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[] = "$FreeBSD: head/lib/msun/src/e_sqrtf.c 97409 2002-05-28 17:51:46Z alfred $"; 18#endif 19 20#include "math.h" 21#include "math_private.h" 22 23static const float one = 1.0, tiny=1.0e-30; 24 25 float __ieee754_sqrtf(float x) 26{ 27 float z; 28 int32_t sign = (int)0x80000000; 29 int32_t ix,s,q,m,t,i; 30 u_int32_t r; 31 32 GET_FLOAT_WORD(ix,x); 33 34 /* take care of Inf and NaN */ 35 if((ix&0x7f800000)==0x7f800000) { 36 return x*x+x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf 37 sqrt(-inf)=sNaN */ 38 } 39 /* take care of zero */ 40 if(ix<=0) { 41 if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */ 42 else if(ix<0) 43 return (x-x)/(x-x); /* sqrt(-ve) = sNaN */ 44 } 45 /* normalize x */ 46 m = (ix>>23); 47 if(m==0) { /* subnormal x */ 48 for(i=0;(ix&0x00800000)==0;i++) ix<<=1; 49 m -= i-1; 50 } 51 m -= 127; /* unbias exponent */ 52 ix = (ix&0x007fffff)|0x00800000; 53 if(m&1) /* odd m, double x to make it even */ 54 ix += ix; 55 m >>= 1; /* m = [m/2] */ 56 57 /* generate sqrt(x) bit by bit */ 58 ix += ix; 59 q = s = 0; /* q = sqrt(x) */ 60 r = 0x01000000; /* r = moving bit from right to left */ 61 62 while(r!=0) { 63 t = s+r; 64 if(t<=ix) { 65 s = t+r; 66 ix -= t; 67 q += r; 68 } 69 ix += ix; 70 r>>=1; 71 } 72 73 /* use floating add to find out rounding direction */ 74 if(ix!=0) { 75 z = one-tiny; /* trigger inexact flag */ 76 if (z>=one) { 77 z = one+tiny; 78 if (z>one) 79 q += 2; 80 else 81 q += (q&1); 82 } 83 } 84 ix = (q>>1)+0x3f000000; 85 ix += (m <<23); 86 SET_FLOAT_WORD(z,ix); 87 return z; 88} 89