e_sqrtf.c (2023B)
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 17 static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_sqrtf.c,v 1.7 2002/05/28 18:15:04 alfred Exp $"; 18 #endif 19 20 #include "math.h" 21 #include "math_private.h" 22 23 static const float one = 1.0, tiny=1.0e-30; 24 25 float 26 __ieee754_sqrtf(float x) 27 { 28 float z; 29 int32_t sign = (int)0x80000000; 30 int32_t ix,s,q,m,t,i; 31 u_int32_t r; 32 33 GET_FLOAT_WORD(ix,x); 34 35 /* take care of Inf and NaN */ 36 if((ix&0x7f800000)==0x7f800000) { 37 return x*x+x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf 38 sqrt(-inf)=sNaN */ 39 } 40 /* take care of zero */ 41 if(ix<=0) { 42 if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */ 43 else if(ix<0) 44 return (x-x)/(x-x); /* sqrt(-ve) = sNaN */ 45 } 46 /* normalize x */ 47 m = (ix>>23); 48 if(m==0) { /* subnormal x */ 49 for(i=0;(ix&0x00800000)==0;i++) ix<<=1; 50 m -= i-1; 51 } 52 m -= 127; /* unbias exponent */ 53 ix = (ix&0x007fffff)|0x00800000; 54 if(m&1) /* odd m, double x to make it even */ 55 ix += ix; 56 m >>= 1; /* m = [m/2] */ 57 58 /* generate sqrt(x) bit by bit */ 59 ix += ix; 60 q = s = 0; /* q = sqrt(x) */ 61 r = 0x01000000; /* r = moving bit from right to left */ 62 63 while(r!=0) { 64 t = s+r; 65 if(t<=ix) { 66 s = t+r; 67 ix -= t; 68 q += r; 69 } 70 ix += ix; 71 r>>=1; 72 } 73 74 /* use floating add to find out rounding direction */ 75 if(ix!=0) { 76 z = one-tiny; /* trigger inexact flag */ 77 if (z>=one) { 78 z = one+tiny; 79 if (z>one) 80 q += 2; 81 else 82 q += (q&1); 83 } 84 } 85 ix = (q>>1)+0x3f000000; 86 ix += (m <<23); 87 SET_FLOAT_WORD(z,ix); 88 return z; 89 }