1 /* IEEE754 floating point arithmetic 2 * single precision square root 3 */ 4 /* 5 * MIPS floating point support 6 * Copyright (C) 1994-2000 Algorithmics Ltd. 7 * 8 * This program is free software; you can distribute it and/or modify it 9 * under the terms of the GNU General Public License (Version 2) as 10 * published by the Free Software Foundation. 11 * 12 * This program is distributed in the hope it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 * for more details. 16 * 17 * You should have received a copy of the GNU General Public License along 18 * with this program; if not, write to the Free Software Foundation, Inc., 19 * 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 */ 21 22 #include "ieee754sp.h" 23 24 union ieee754sp ieee754sp_sqrt(union ieee754sp x) 25 { 26 int ix, s, q, m, t, i; 27 unsigned int r; 28 COMPXSP; 29 30 /* take care of Inf and NaN */ 31 32 EXPLODEXSP; 33 ieee754_clearcx(); 34 FLUSHXSP; 35 36 /* x == INF or NAN? */ 37 switch (xc) { 38 case IEEE754_CLASS_SNAN: 39 return ieee754sp_nanxcpt(x); 40 41 case IEEE754_CLASS_QNAN: 42 /* sqrt(Nan) = Nan */ 43 return x; 44 45 case IEEE754_CLASS_ZERO: 46 /* sqrt(0) = 0 */ 47 return x; 48 49 case IEEE754_CLASS_INF: 50 if (xs) { 51 /* sqrt(-Inf) = Nan */ 52 ieee754_setcx(IEEE754_INVALID_OPERATION); 53 return ieee754sp_indef(); 54 } 55 /* sqrt(+Inf) = Inf */ 56 return x; 57 58 case IEEE754_CLASS_DNORM: 59 case IEEE754_CLASS_NORM: 60 if (xs) { 61 /* sqrt(-x) = Nan */ 62 ieee754_setcx(IEEE754_INVALID_OPERATION); 63 return ieee754sp_indef(); 64 } 65 break; 66 } 67 68 ix = x.bits; 69 70 /* normalize x */ 71 m = (ix >> 23); 72 if (m == 0) { /* subnormal x */ 73 for (i = 0; (ix & 0x00800000) == 0; i++) 74 ix <<= 1; 75 m -= i - 1; 76 } 77 m -= 127; /* unbias exponent */ 78 ix = (ix & 0x007fffff) | 0x00800000; 79 if (m & 1) /* odd m, double x to make it even */ 80 ix += ix; 81 m >>= 1; /* m = [m/2] */ 82 83 /* generate sqrt(x) bit by bit */ 84 ix += ix; 85 s = 0; 86 q = 0; /* q = sqrt(x) */ 87 r = 0x01000000; /* r = moving bit from right to left */ 88 89 while (r != 0) { 90 t = s + r; 91 if (t <= ix) { 92 s = t + r; 93 ix -= t; 94 q += r; 95 } 96 ix += ix; 97 r >>= 1; 98 } 99 100 if (ix != 0) { 101 ieee754_setcx(IEEE754_INEXACT); 102 switch (ieee754_csr.rm) { 103 case FPU_CSR_RU: 104 q += 2; 105 break; 106 case FPU_CSR_RN: 107 q += (q & 1); 108 break; 109 } 110 } 111 ix = (q >> 1) + 0x3f000000; 112 ix += (m << 23); 113 x.bits = ix; 114 return x; 115 } 116