1 // SPDX-License-Identifier: GPL-2.0-only 2 /* IEEE754 floating point arithmetic 3 * single precision square root 4 */ 5 /* 6 * MIPS floating point support 7 * Copyright (C) 1994-2000 Algorithmics Ltd. 8 */ 9 10 #include "ieee754sp.h" 11 ieee754sp_sqrt(union ieee754sp x)12union ieee754sp ieee754sp_sqrt(union ieee754sp x) 13 { 14 int ix, s, q, m, t, i; 15 unsigned int r; 16 COMPXSP; 17 18 /* take care of Inf and NaN */ 19 20 EXPLODEXSP; 21 ieee754_clearcx(); 22 FLUSHXSP; 23 24 /* x == INF or NAN? */ 25 switch (xc) { 26 case IEEE754_CLASS_SNAN: 27 return ieee754sp_nanxcpt(x); 28 29 case IEEE754_CLASS_QNAN: 30 /* sqrt(Nan) = Nan */ 31 return x; 32 33 case IEEE754_CLASS_ZERO: 34 /* sqrt(0) = 0 */ 35 return x; 36 37 case IEEE754_CLASS_INF: 38 if (xs) { 39 /* sqrt(-Inf) = Nan */ 40 ieee754_setcx(IEEE754_INVALID_OPERATION); 41 return ieee754sp_indef(); 42 } 43 /* sqrt(+Inf) = Inf */ 44 return x; 45 46 case IEEE754_CLASS_DNORM: 47 case IEEE754_CLASS_NORM: 48 if (xs) { 49 /* sqrt(-x) = Nan */ 50 ieee754_setcx(IEEE754_INVALID_OPERATION); 51 return ieee754sp_indef(); 52 } 53 break; 54 } 55 56 ix = x.bits; 57 58 /* normalize x */ 59 m = (ix >> 23); 60 if (m == 0) { /* subnormal x */ 61 for (i = 0; (ix & 0x00800000) == 0; i++) 62 ix <<= 1; 63 m -= i - 1; 64 } 65 m -= 127; /* unbias exponent */ 66 ix = (ix & 0x007fffff) | 0x00800000; 67 if (m & 1) /* odd m, double x to make it even */ 68 ix += ix; 69 m >>= 1; /* m = [m/2] */ 70 71 /* generate sqrt(x) bit by bit */ 72 ix += ix; 73 s = 0; 74 q = 0; /* q = sqrt(x) */ 75 r = 0x01000000; /* r = moving bit from right to left */ 76 77 while (r != 0) { 78 t = s + r; 79 if (t <= ix) { 80 s = t + r; 81 ix -= t; 82 q += r; 83 } 84 ix += ix; 85 r >>= 1; 86 } 87 88 if (ix != 0) { 89 ieee754_setcx(IEEE754_INEXACT); 90 switch (ieee754_csr.rm) { 91 case FPU_CSR_RU: 92 q += 2; 93 break; 94 case FPU_CSR_RN: 95 q += (q & 1); 96 break; 97 } 98 } 99 ix = (q >> 1) + 0x3f000000; 100 ix += (m << 23); 101 x.bits = ix; 102 return x; 103 } 104