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perf: optimize bigint compare() with static ints #1856

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perf: optimize bigint compare() with static ints #1856

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34 changes: 27 additions & 7 deletions lib/Support/BigIntSupport.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -150,6 +150,10 @@ OperationStatus initWithBytes(
return OperationStatus::RETURNED;
}

bool isZero(ImmutableBigIntRef lhs) {
return lhs.numDigits == 0;
}

bool isNegative(ImmutableBigIntRef src) {
return src.numDigits > 0 &&
static_cast<SignedBigIntDigitType>(src.digits[src.numDigits - 1]) < 0;
Expand Down Expand Up @@ -1028,7 +1032,7 @@ std::optional<ParsedBigInt> ParsedBigInt::parsedBigIntFromNumericValue(
std::string toString(ImmutableBigIntRef src, uint8_t radix) {
assert(radix >= 2 && radix <= 36);

if (compare(src, 0) == 0) {
if (isZero(src)) {
return "0";
}

Expand Down Expand Up @@ -1148,6 +1152,22 @@ ImmutableBigIntRef makeImmutableRefFromSignedDigit(
} // namespace

int compare(ImmutableBigIntRef lhs, SignedBigIntDigitType rhs) {
const int kLhsGreater = 1;
const int kRhsGreater = -kLhsGreater;

if (rhs == 0) {
if (isZero(lhs)) return 0;
return isNegative(lhs) ? kRhsGreater : kLhsGreater;
} else if (rhs == 1) {
if (isZero(lhs) || isNegative(lhs)) return kRhsGreater;
if (lhs.numDigits > 1) return kLhsGreater;
return static_cast<SignedBigIntDigitType>(lhs.digits[0]) == 1 ? 0 : kLhsGreater;
} else if (rhs == -1) {
if (!isNegative(lhs)) return kLhsGreater;
if (lhs.numDigits > 1) return kRhsGreater;
return static_cast<SignedBigIntDigitType>(lhs.digits[0]) == -1 ? 0 : kRhsGreater;
}

// wrapping rhs in a ImmutableBigIntRef is safe -- rhs outlives the temporary.
return compare(lhs, makeImmutableRefFromSignedDigit(rhs));
}
Expand Down Expand Up @@ -1386,7 +1406,7 @@ OperationStatus unaryMinus(MutableBigIntRef dst, ImmutableBigIntRef src) {
assert(
((isNegative(ImmutableBigIntRef{dst.digits, dst.numDigits}) !=
isNegative(src)) ||
compare(src, 0) == 0) &&
isZero(src)) &&
"unaryMinus overflow");
return OperationStatus::RETURNED;
}
Expand Down Expand Up @@ -1773,7 +1793,7 @@ static OperationStatus compute(
rem.numDigits = resultSize;

// Signal division by zero.
if (compare(rhs, 0) == 0) {
if (isZero(rhs)) {
return OperationStatus::DIVISION_BY_ZERO;
}

Expand Down Expand Up @@ -2061,7 +2081,7 @@ OperationStatus exponentiateSlowPath(
// include runningSquare in the result if lhs_i is 1.
if ((exponent & 1) != 0) {
nextResult.resetRefNumDigits();
if (compare(result, 0) == 0) {
if (isZero(result)) {
res = initWithDigits(nextResult, runningSquare);
} else {
res = multiply(nextResult, result, runningSquare);
Expand Down Expand Up @@ -2093,7 +2113,7 @@ OperationStatus exponentiate(
MutableBigIntRef dst,
ImmutableBigIntRef lhs,
ImmutableBigIntRef rhs) {
if (compare(rhs, 0) < 0) {
if (isNegative(rhs)) {
return OperationStatus::NEGATIVE_EXPONENT;
}

Expand All @@ -2110,7 +2130,7 @@ OperationStatus exponentiate(
// 4. If |lhs| == 2, use a fast-path for that.
// 5. Fall back to the slow path.
OperationStatus res = OperationStatus::RETURNED;
if (compare(rhs, 0) == 0) {
if (isZero(rhs)) {
// lhs ** 0 => 1, for all lhs
// N.B.: JS defines 0n ** 0n == 1.
if (dst.numDigits < 1) {
Expand All @@ -2119,7 +2139,7 @@ OperationStatus exponentiate(
dst.numDigits = 1;
dst.digits[0] = 1;
}
} else if (compare(lhs, 0) == 0) {
} else if (isZero(lhs)) {
// 0 ** rhs => 0, for rhs > 0
dst.numDigits = 0;
} else if (dst.numDigits < 1) {
Expand Down