1 /* ef_sqrtf.c -- float version of e_sqrt.c. 2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian (at) 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 #include "fdlibm.h" 17 18 #ifdef __STDC__ 19 static const float one = 1.0, tiny=1.0e-30; 20 #else 21 static float one = 1.0, tiny=1.0e-30; 22 #endif 23 24 #ifdef __STDC__ 25 float __ieee754_sqrtf(float x) 26 #else 27 float __ieee754_sqrtf(x) 28 float x; 29 #endif 30 { 31 float z; 32 __uint32_t r,hx; 33 __int32_t ix,s,q,m,t,i; 34 35 GET_FLOAT_WORD(ix,x); 36 hx = ix&0x7fffffff; 37 38 /* take care of Inf and NaN */ 39 if(!FLT_UWORD_IS_FINITE(hx)) 40 return x*x+x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf 41 sqrt(-inf)=sNaN */ 42 /* take care of zero and -ves */ 43 if(FLT_UWORD_IS_ZERO(hx)) return x;/* sqrt(+-0) = +-0 */ 44 if(ix<0) return (x-x)/(x-x); /* sqrt(-ve) = sNaN */ 45 46 /* normalize x */ 47 m = (ix>>23); 48 if(FLT_UWORD_IS_SUBNORMAL(hx)) { /* subnormal x */ 49 for(i=0;(ix&0x00800000L)==0;i++) ix<<=1; 50 m -= i-1; 51 } 52 m -= 127; /* unbias exponent */ 53 ix = (ix&0x007fffffL)|0x00800000L; 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 = 0x01000000L; /* 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)+0x3f000000L; 86 ix += (m <<23); 87 SET_FLOAT_WORD(z,ix); 88 return z; 89 } 90
