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Simplify and document RoundDoubleToAPInt.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34648 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Spencer 2007-02-27 01:28:10 +00:00
parent 532d0ce208
commit 30f44f3287
1 changed files with 15 additions and 3 deletions
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18
lib/Support/APInt.cpp
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@ -803,15 +803,27 @@ APInt llvm::APIntOps::RoundDoubleToAPInt(double Double) {
uint64_t I;
} T;
T.D = Double;
// Get the sign bit from the highest order bit
bool isNeg = T.I >> 63;
// Get the 11-bit exponent and adjust for the 1023 bit bias
int64_t exp = ((T.I >> 52) & 0x7ff) - 1023;
// If the exponent is negative, the value is < 0 so just return 0.
if (exp < 0)
return APInt(64ull, 0u);
uint64_t mantissa = ((T.I << 12) >> 12) | (1ULL << 52);
return APInt(64u, 0u);
// Extract the mantissa by clearing the top 12 bits (sign + exponent).
uint64_t mantissa = (T.I & (~0ULL >> 12)) | 1ULL << 52;
// If the exponent doesn't shift all bits out of the mantissa
if (exp < 52)
return isNeg ? -APInt(64u, mantissa >> (52 - exp)) :
APInt(64u, mantissa >> (52 - exp));
APInt Tmp(exp + 1, mantissa);
// Otherwise, we have to shift the mantissa bits up to the right location
APInt Tmp(exp+1, mantissa);
Tmp = Tmp.shl(exp - 52);
return isNeg ? -Tmp : Tmp;
}