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105 lines
3.2 KiB
C
105 lines
3.2 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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/* int64_t __fixunstfdi(long double x);
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* This file implements the PowerPC 128-bit double-double -> int64_t conversion
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*/
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#include "DD.h"
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#include "../int_math.h"
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uint64_t __fixtfdi(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 absHighWord = (uint32_t)(hibits.x >> 32) & UINT32_C(0x7fffffff);
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const uint32_t absHighWordMinusOne = absHighWord - UINT32_C(0x3ff00000);
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/* If (1.0 - tiny) <= input < 0x1.0p63: */
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if (UINT32_C(0x03f00000) > absHighWordMinusOne)
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{
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/* Do an unsigned conversion of the absolute value, then restore the sign. */
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const int unbiasedHeadExponent = absHighWordMinusOne >> 20;
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int64_t result = hibits.x & INT64_C(0x000fffffffffffff); /* mantissa(hi) */
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result |= INT64_C(0x0010000000000000); /* matissa(hi) with implicit bit */
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result <<= 10; /* mantissa(hi) with one zero preceding bit. */
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const int64_t hiNegationMask = ((int64_t)(hibits.x)) >> 63;
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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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/* We need to negate it if head and tail have different signs. */
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const int64_t loNegationMask = ((int64_t)(lobits.x)) >> 63;
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const int64_t negationMask = loNegationMask ^ hiNegationMask;
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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 10 that we shifted the head mantissa by.
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*/
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tailMantissa >>= (unbiasedHeadExponent - (biasedTailExponent - (1023 - 10)));
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result += tailMantissa;
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}
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result >>= (62 - unbiasedHeadExponent);
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/* Restore the sign of the result and return */
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result = (result ^ hiNegationMask) - hiNegationMask;
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return result;
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}
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/* Edge cases handled here: */
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/* |x| < 1, result is zero. */
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if (1.0 > crt_fabs(x.s.hi))
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return INT64_C(0);
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/* x very close to INT64_MIN, care must be taken to see which side we are on. */
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if (x.s.hi == -0x1.0p63) {
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int64_t result = INT64_MIN;
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if (0.0 < x.s.lo)
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{
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/* If the tail is positive, the correct result is something other than INT64_MIN.
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* we'll need to figure out what it is.
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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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/* Now we negate the tailMantissa */
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tailMantissa = (tailMantissa ^ INT64_C(-1)) + INT64_C(1);
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/* And shift it by the appropriate amount */
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const int biasedTailExponent = (int)(lobits.x >> 52) & 0x7ff;
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tailMantissa >>= 1075 - biasedTailExponent;
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result -= tailMantissa;
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}
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return result;
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}
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/* Signed overflows, infinities, and NaNs */
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if (x.s.hi > 0.0)
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return INT64_MAX;
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else
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return INT64_MIN;
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}
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