1 /* This file is distributed under the University of Illinois Open Source 2 * License. See LICENSE.TXT for details. 3 */ 4 5 /* uint64_t __fixunstfdi(long double x); */ 6 /* This file implements the PowerPC 128-bit double-double -> uint64_t conversion */ 7 8 #include "DD.h" 9 #include <stdint.h> 10 11 uint64_t __fixunstfdi(long double input) 12 { 13 const DD x = { .ld = input }; 14 const doublebits hibits = { .d = x.s.hi }; 15 16 const uint32_t highWordMinusOne = (uint32_t)(hibits.x >> 32) - UINT32_C(0x3ff00000); 17 18 /* If (1.0 - tiny) <= input < 0x1.0p64: */ 19 if (UINT32_C(0x04000000) > highWordMinusOne) 20 { 21 const int unbiasedHeadExponent = highWordMinusOne >> 20; 22 23 uint64_t result = hibits.x & UINT64_C(0x000fffffffffffff); /* mantissa(hi) */ 24 result |= UINT64_C(0x0010000000000000); /* matissa(hi) with implicit bit */ 25 result <<= 11; /* mantissa(hi) left aligned in the int64 field. */ 26 27 /* If the tail is non-zero, we need to patch in the tail bits. */ 28 if (0.0 != x.s.lo) 29 { 30 const doublebits lobits = { .d = x.s.lo }; 31 int64_t tailMantissa = lobits.x & INT64_C(0x000fffffffffffff); 32 tailMantissa |= INT64_C(0x0010000000000000); 33 34 /* At this point we have the mantissa of |tail| */ 35 36 const int64_t negationMask = ((int64_t)(lobits.x)) >> 63; 37 tailMantissa = (tailMantissa ^ negationMask) - negationMask; 38 39 /* Now we have the mantissa of tail as a signed 2s-complement integer */ 40 41 const int biasedTailExponent = (int)(lobits.x >> 52) & 0x7ff; 42 43 /* Shift the tail mantissa into the right position, accounting for the 44 * bias of 11 that we shifted the head mantissa by. 45 */ 46 tailMantissa >>= (unbiasedHeadExponent - (biasedTailExponent - (1023 - 11))); 47 48 result += tailMantissa; 49 } 50 51 result >>= (63 - unbiasedHeadExponent); 52 return result; 53 } 54 55 /* Edge cases are handled here, with saturation. */ 56 if (1.0 > x.s.hi) 57 return UINT64_C(0); 58 else 59 return UINT64_MAX; 60 } 61
