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-rw-r--r--lib/ppc/fixunstfdi.c58
1 files changed, 58 insertions, 0 deletions
diff --git a/lib/ppc/fixunstfdi.c b/lib/ppc/fixunstfdi.c
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+++ b/lib/ppc/fixunstfdi.c
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+// 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;
+}