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Clean up the divide and remainder logic a bit (exit early). Use more 

meaningful variable names. Add comments to document the flow.

llvm-svn: 34362
This commit is contained in:
Reid Spencer 2007-02-17 02:07:07 +00:00
parent 3ae936ce69
commit 3986776fbd
1 changed files with 90 additions and 65 deletions
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155
llvm/lib/Support/APInt.cpp
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@ -213,7 +213,8 @@ static void div(unsigned zds[], unsigned nx, unsigned y[], unsigned ny) {
// Knuth's j == our nx-j.
// Knuth's u[j:j+n] == our zds[j:j-ny].
unsigned qhat; // treated as unsigned
if (zds[j] == y[ny-1]) qhat = -1U; // 0xffffffff
if (zds[j] == y[ny-1])
qhat = -1U; // 0xffffffff
else {
uint64_t w = (((uint64_t)(zds[j])) << 32) +
((uint64_t)zds[j-1] & 0xffffffffL);
@ -1137,76 +1138,100 @@ APInt APInt::shl(unsigned shiftAmt) const {
/// @brief Unsigned division function for APInt.
APInt APInt::udiv(const APInt& RHS) const {
assert(BitWidth == RHS.BitWidth && "Bit widths must be the same");
APInt API(*this);
unsigned first = RHS.getActiveBits();
unsigned ylen = !first ? 0 : APInt::whichWord(first - 1) + 1;
assert(ylen && "Divided by zero???");
if (API.isSingleWord()) {
API.VAL = RHS.isSingleWord() ? (API.VAL / RHS.VAL) :
(ylen > 1 ? 0 : API.VAL / RHS.pVal[0]);
} else {
unsigned first2 = API.getActiveBits();
unsigned xlen = !first2 ? 0 : APInt::whichWord(first2 - 1) + 1;
if (!xlen)
return API;
else if (xlen < ylen || API.ult(RHS))
memset(API.pVal, 0, API.getNumWords() * 8);
else if (API == RHS) {
memset(API.pVal, 0, API.getNumWords() * 8);
API.pVal[0] = 1;
} else if (xlen == 1)
API.pVal[0] /= RHS.isSingleWord() ? RHS.VAL : RHS.pVal[0];
else {
APInt X(BitWidth, 0);
APInt Y(BitWidth, 0);
if (unsigned nshift = 63 - (first - 1) % 64) {
Y = APIntOps::shl(RHS, nshift);
X = APIntOps::shl(API, nshift);
++xlen;
}
div((unsigned*)X.pVal, xlen*2-1,
(unsigned*)(Y.isSingleWord() ? &Y.VAL : Y.pVal), ylen*2);
memset(API.pVal, 0, API.getNumWords() * 8);
memcpy(API.pVal, X.pVal + ylen, (xlen - ylen) * 8);
}
// First, deal with the easy case
if (isSingleWord()) {
assert(RHS.VAL != 0 && "Divide by zero?");
return APInt(BitWidth, VAL / RHS.VAL);
}
return API;
// Make a temporary to hold the result
APInt Result(*this);
// Get some facts about the LHS and RHS number of bits and words
unsigned rhsBits = RHS.getActiveBits();
unsigned rhsWords = !rhsBits ? 0 : (APInt::whichWord(rhsBits - 1) + 1);
assert(rhsWords && "Divided by zero???");
unsigned lhsBits = Result.getActiveBits();
unsigned lhsWords = !lhsBits ? 0 : (APInt::whichWord(lhsBits - 1) + 1);
// Deal with some degenerate cases
if (!lhsWords)
return Result; // 0 / X == 0
else if (lhsWords < rhsWords || Result.ult(RHS))
// X / Y with X < Y == 0
memset(Result.pVal, 0, Result.getNumWords() * 8);
else if (Result == RHS) {
// X / X == 1
memset(Result.pVal, 0, Result.getNumWords() * 8);
Result.pVal[0] = 1;
} else if (lhsWords == 1)
// All high words are zero, just use native divide
Result.pVal[0] /= RHS.pVal[0];
else {
// Compute it the hard way ..
APInt X(BitWidth, 0);
APInt Y(BitWidth, 0);
if (unsigned nshift = 63 - ((rhsBits - 1) % 64 )) {
Y = APIntOps::shl(RHS, nshift);
X = APIntOps::shl(Result, nshift);
++lhsWords;
}
div((unsigned*)X.pVal, lhsWords * 2 - 1, (unsigned*)Y.pVal, rhsWords*2);
memset(Result.pVal, 0, Result.getNumWords() * 8);
memcpy(Result.pVal, X.pVal + rhsWords, (lhsWords - rhsWords) * 8);
}
return Result;
}
/// Unsigned remainder operation on APInt.
/// @brief Function for unsigned remainder operation.
APInt APInt::urem(const APInt& RHS) const {
assert(BitWidth == RHS.BitWidth && "Bit widths must be the same");
APInt API(*this);
unsigned first = RHS.getActiveBits();
unsigned ylen = !first ? 0 : APInt::whichWord(first - 1) + 1;
assert(ylen && "Performing remainder operation by zero ???");
if (API.isSingleWord()) {
API.VAL = RHS.isSingleWord() ? (API.VAL % RHS.VAL) :
(ylen > 1 ? API.VAL : API.VAL % RHS.pVal[0]);
} else {
unsigned first2 = API.getActiveBits();
unsigned xlen = !first2 ? 0 : API.whichWord(first2 - 1) + 1;
if (!xlen || xlen < ylen || API.ult(RHS))
return API;
else if (API == RHS)
memset(API.pVal, 0, API.getNumWords() * 8);
else if (xlen == 1)
API.pVal[0] %= RHS.isSingleWord() ? RHS.VAL : RHS.pVal[0];
else {
APInt X((xlen+1)*64, 0), Y(ylen*64, 0);
unsigned nshift = 63 - (first - 1) % 64;
if (nshift) {
APIntOps::shl(Y, nshift);
APIntOps::shl(X, nshift);
}
div((unsigned*)X.pVal, xlen*2-1,
(unsigned*)(Y.isSingleWord() ? &Y.VAL : Y.pVal), ylen*2);
memset(API.pVal, 0, API.getNumWords() * 8);
for (unsigned i = 0; i < ylen-1; ++i)
API.pVal[i] = (X.pVal[i] >> nshift) | (X.pVal[i+1] << (64 - nshift));
API.pVal[ylen-1] = X.pVal[ylen-1] >> nshift;
}
if (isSingleWord()) {
assert(RHS.VAL != 0 && "Remainder by zero?");
return APInt(BitWidth, VAL % RHS.VAL);
}
return API;
// Make a temporary to hold the result
APInt Result(*this);
// Get some facts about the RHS
unsigned rhsBits = RHS.getActiveBits();
unsigned rhsWords = !rhsBits ? 0 : (APInt::whichWord(rhsBits - 1) + 1);
assert(rhsWords && "Performing remainder operation by zero ???");
// Get some facts about the LHS
unsigned lhsBits = Result.getActiveBits();
unsigned lhsWords = !lhsBits ? 0 : (Result.whichWord(lhsBits - 1) + 1);
// Check the degenerate cases
if (lhsWords == 0)
// 0 % Y == 0
memset(Result.pVal, 0, Result.getNumWords() * 8);
else if (lhsWords < rhsWords || Result.ult(RHS))
// X % Y == X iff X < Y
return Result;
else if (Result == RHS)
// X % X == 0;
memset(Result.pVal, 0, Result.getNumWords() * 8);
else if (lhsWords == 1)
// All high words are zero, just use native remainder
Result.pVal[0] %= RHS.pVal[0];
else {
// Do it the hard way
APInt X((lhsWords+1)*64, 0);
APInt Y(rhsWords*64, 0);
unsigned nshift = 63 - (rhsBits - 1) % 64;
if (nshift) {
APIntOps::shl(Y, nshift);
APIntOps::shl(X, nshift);
}
div((unsigned*)X.pVal, rhsWords*2-1, (unsigned*)Y.pVal, rhsWords*2);
memset(Result.pVal, 0, Result.getNumWords() * 8);
for (unsigned i = 0; i < rhsWords-1; ++i)
Result.pVal[i] = (X.pVal[i] >> nshift) | (X.pVal[i+1] << (64 - nshift));
Result.pVal[rhsWords-1] = X.pVal[rhsWords-1] >> nshift;
}
return Result;
}