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guard zero digit count in GenerateCountedDigits #306

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5 changes: 5 additions & 0 deletions double-conversion/bignum-dtoa.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -284,6 +284,11 @@ static void GenerateCountedDigits(int count, int* decimal_point,
Bignum* numerator, Bignum* denominator,
Vector<char> buffer, int* length) {
DOUBLE_CONVERSION_ASSERT(count >= 0);
if (count == 0) {
// No digits requested. The "last digit" store below would write buffer[-1].
*length = 0;
return;
}
for (int i = 0; i < count - 1; ++i) {
uint16_t digit;
digit = numerator->DivideModuloIntBignum(*denominator);
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20 changes: 20 additions & 0 deletions test/cctest/test-bignum-dtoa.cc
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Expand Up @@ -258,6 +258,26 @@ TEST(BignumDtoaVariousDoubles) {
}


TEST(BignumDtoaZeroPrecision) {
// Requesting zero precision digits must produce an empty representation
// without storing the "last digit" at buffer[-1]. A sentinel byte sits
// immediately before the output buffer to catch that store.
char container[kBufferSize];
container[0] = '@';
Vector<char> buffer(container + 1, kBufferSize - 1);
int length;
int point;

BignumDtoa(1.0, BIGNUM_DTOA_PRECISION, 0, buffer, &length, &point);
CHECK_EQ(0, length);
CHECK(container[0] == '@');

BignumDtoa(123.456, BIGNUM_DTOA_PRECISION, 0, buffer, &length, &point);
CHECK_EQ(0, length);
CHECK(container[0] == '@');
}


TEST(BignumDtoaShortestVariousFloats) {
char buffer_container[kBufferSize];
Vector<char> buffer(buffer_container, kBufferSize);
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