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Diffstat (limited to 'lib/ppc/fixunstfdi.c')
-rw-r--r-- | lib/ppc/fixunstfdi.c | 58 |
1 files changed, 58 insertions, 0 deletions
diff --git a/lib/ppc/fixunstfdi.c b/lib/ppc/fixunstfdi.c new file mode 100644 index 000000000..35ce3a912 --- /dev/null +++ b/lib/ppc/fixunstfdi.c @@ -0,0 +1,58 @@ +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. + +// uint64_t __fixunstfdi(long double x); +// This file implements the PowerPC 128-bit double-double -> uint64_t conversion + +#include "DD.h" +#include <stdint.h> + +uint64_t __fixunstfdi(long double input) +{ + const DD x = { .ld = input }; + const doublebits hibits = { .d = x.hi }; + + const uint32_t highWordMinusOne = (uint32_t)(hibits.x >> 32) - UINT32_C(0x3ff00000); + + // If (1.0 - tiny) <= input < 0x1.0p64: + if (UINT32_C(0x04000000) > highWordMinusOne) + { + const int unbiasedHeadExponent = highWordMinusOne >> 20; + + uint64_t result = hibits.x & UINT64_C(0x000fffffffffffff); // mantissa(hi) + result |= UINT64_C(0x0010000000000000); // matissa(hi) with implicit bit + result <<= 11; // mantissa(hi) left aligned in the int64 field. + + // If the tail is non-zero, we need to patch in the tail bits. + if (0.0 != x.lo) + { + const doublebits lobits = { .d = x.lo }; + int64_t tailMantissa = lobits.x & INT64_C(0x000fffffffffffff); + tailMantissa |= INT64_C(0x0010000000000000); + + // At this point we have the mantissa of |tail| + + const int64_t negationMask = ((int64_t)(lobits.x)) >> 63; + tailMantissa = (tailMantissa ^ negationMask) - negationMask; + + // Now we have the mantissa of tail as a signed 2s-complement integer + + const int biasedTailExponent = (int)(lobits.x >> 52) & 0x7ff; + + // Shift the tail mantissa into the right position, accounting for the + // bias of 11 that we shifted the head mantissa by. + tailMantissa >>= (unbiasedHeadExponent - (biasedTailExponent - (1023 - 11))); + + result += tailMantissa; + } + + result >>= (63 - unbiasedHeadExponent); + return result; + } + + // Edge cases are handled here, with saturation. + if (1.0 > x.hi) + return UINT64_C(0); + else + return UINT64_MAX; +} |