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Fix ashr for bitwidths > 64. This is now validated up to 1024 bits.

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llvm-svn: 34852
This commit is contained in:
Reid Spencer 2007-03-02 22:39:11 +00:00
parent af46a0e4a2
commit 3e3980a403
1 changed files with 49 additions and 33 deletions
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82
lib/Support/APInt.cpp
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@ -1007,6 +1007,11 @@ APInt &APInt::sextOrTrunc(uint32_t width) {
/// @brief Arithmetic right-shift function.
APInt APInt::ashr(uint32_t shiftAmt) const {
assert(shiftAmt <= BitWidth && "Invalid shift amount");
// Handle a degenerate case
if (shiftAmt == 0)
return *this;
// Handle single word shifts with built-in ashr
if (isSingleWord()) {
if (shiftAmt == BitWidth)
return APInt(BitWidth, 0); // undefined
@ -1017,9 +1022,9 @@ APInt APInt::ashr(uint32_t shiftAmt) const {
}
}
// If all the bits were shifted out, the result is 0 or -1. This avoids issues
// with shifting by the size of the integer type, which produces undefined
// results.
// If all the bits were shifted out, the result is, technically, undefined.
// We return -1 if it was negative, 0 otherwise. We check this early to avoid
// issues in the algorithm below.
if (shiftAmt == BitWidth)
if (isNegative())
return APInt(BitWidth, -1ULL);
@ -1029,42 +1034,53 @@ APInt APInt::ashr(uint32_t shiftAmt) const {
// Create some space for the result.
uint64_t * val = new uint64_t[getNumWords()];
// If we are shifting less than a word, compute the shift with a simple carry
if (shiftAmt < APINT_BITS_PER_WORD) {
uint64_t carry = 0;
for (int i = getNumWords()-1; i >= 0; --i) {
val[i] = (pVal[i] >> shiftAmt) | carry;
carry = pVal[i] << (APINT_BITS_PER_WORD - shiftAmt);
}
return APInt(val, BitWidth).clearUnusedBits();
}
// Compute some values needed by the remaining shift algorithms
uint32_t wordShift = shiftAmt % APINT_BITS_PER_WORD;
uint32_t offset = shiftAmt / APINT_BITS_PER_WORD;
// Compute some values needed by the following shift algorithms
uint32_t wordShift = shiftAmt % APINT_BITS_PER_WORD; // bits to shift per word
uint32_t offset = shiftAmt / APINT_BITS_PER_WORD; // word offset for shift
uint32_t breakWord = getNumWords() - 1 - offset; // last word affected
uint32_t bitsInWord = whichBit(BitWidth); // how many bits in last word?
if (bitsInWord == 0)
bitsInWord = APINT_BITS_PER_WORD;
// If we are shifting whole words, just move whole words
if (wordShift == 0) {
for (uint32_t i = 0; i < getNumWords() - offset; ++i)
val[i] = pVal[i+offset];
for (uint32_t i = getNumWords()-offset; i < getNumWords(); i++)
val[i] = (isNegative() ? -1ULL : 0);
return APInt(val,BitWidth).clearUnusedBits();
// Move the words containing significant bits
for (uint32_t i = 0; i <= breakWord; ++i)
val[i] = pVal[i+offset]; // move whole word
// Adjust the top significant word for sign bit fill, if negative
if (isNegative())
if (bitsInWord < APINT_BITS_PER_WORD)
val[breakWord] |= ~0ULL << bitsInWord; // set high bits
} else {
// Shift the low order words
for (uint32_t i = 0; i < breakWord; ++i) {
// This combines the shifted corresponding word with the low bits from
// the next word (shifted into this word's high bits).
val[i] = (pVal[i+offset] >> wordShift) |
(pVal[i+offset+1] << (APINT_BITS_PER_WORD - wordShift));
}
// Shift the break word. In this case there are no bits from the next word
// to include in this word.
val[breakWord] = pVal[breakWord+offset] >> wordShift;
// Deal with sign extenstion in the break word, and possibly the word before
// it.
if (isNegative())
if (wordShift > bitsInWord) {
if (breakWord > 0)
val[breakWord-1] |=
~0ULL << (APINT_BITS_PER_WORD - (wordShift - bitsInWord));
val[breakWord] |= ~0ULL;
} else
val[breakWord] |= (~0ULL << (bitsInWord - wordShift));
}
// Shift the low order words
uint32_t breakWord = getNumWords() - offset -1;
for (uint32_t i = 0; i < breakWord; ++i)
val[i] = (pVal[i+offset] >> wordShift) |
(pVal[i+offset+1] << (APINT_BITS_PER_WORD - wordShift));
// Shift the break word.
uint32_t SignBit = APINT_BITS_PER_WORD - (BitWidth % APINT_BITS_PER_WORD);
val[breakWord] = uint64_t(
(((int64_t(pVal[breakWord+offset]) << SignBit) >> SignBit) >> wordShift));
// Remaining words are 0 or -1
// Remaining words are 0 or -1, just assign them.
uint64_t fillValue = (isNegative() ? -1ULL : 0);
for (uint32_t i = breakWord+1; i < getNumWords(); ++i)
val[i] = (isNegative() ? -1ULL : 0);
val[i] = fillValue;
return APInt(val, BitWidth).clearUnusedBits();
}