60 lines
1.8 KiB
C
60 lines
1.8 KiB
C
/* This file is distributed under the University of Illinois Open Source
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* License. See LICENSE.TXT for details.
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*/
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/* uint64_t __fixunstfdi(long double x); */
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/* This file implements the PowerPC 128-bit double-double -> uint64_t conversion */
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#include "DD.h"
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uint64_t __fixunstfdi(long double input)
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{
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const DD x = { .ld = input };
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const doublebits hibits = { .d = x.s.hi };
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const uint32_t highWordMinusOne = (uint32_t)(hibits.x >> 32) - UINT32_C(0x3ff00000);
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/* If (1.0 - tiny) <= input < 0x1.0p64: */
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if (UINT32_C(0x04000000) > highWordMinusOne)
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{
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const int unbiasedHeadExponent = highWordMinusOne >> 20;
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uint64_t result = hibits.x & UINT64_C(0x000fffffffffffff); /* mantissa(hi) */
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result |= UINT64_C(0x0010000000000000); /* matissa(hi) with implicit bit */
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result <<= 11; /* mantissa(hi) left aligned in the int64 field. */
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/* If the tail is non-zero, we need to patch in the tail bits. */
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if (0.0 != x.s.lo)
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{
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const doublebits lobits = { .d = x.s.lo };
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int64_t tailMantissa = lobits.x & INT64_C(0x000fffffffffffff);
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tailMantissa |= INT64_C(0x0010000000000000);
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/* At this point we have the mantissa of |tail| */
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const int64_t negationMask = ((int64_t)(lobits.x)) >> 63;
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tailMantissa = (tailMantissa ^ negationMask) - negationMask;
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/* Now we have the mantissa of tail as a signed 2s-complement integer */
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const int biasedTailExponent = (int)(lobits.x >> 52) & 0x7ff;
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/* Shift the tail mantissa into the right position, accounting for the
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* bias of 11 that we shifted the head mantissa by.
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*/
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tailMantissa >>= (unbiasedHeadExponent - (biasedTailExponent - (1023 - 11)));
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result += tailMantissa;
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}
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result >>= (63 - unbiasedHeadExponent);
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return result;
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}
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/* Edge cases are handled here, with saturation. */
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if (1.0 > x.s.hi)
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return UINT64_C(0);
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else
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return UINT64_MAX;
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}
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