261103.1 · 9f2fdfa2a923784a73cc97da9b369edaf4c6c243
Fix BigInt::toString for values larger than 64 bits (#18)
BigInt values wider than 64 bits (for example 2^64, 10^40 or 2^128-1) gave wrong strings from bigintToString. Rework the division loop so it divides in place, resets the remainder on every pass and trims leading zeros. Also correct the per-word character estimate used to reserve the output string.
Add a BigIntToStringMultiWord test that compares the result against the engine's BigInt.prototype.toString for radixes 2-36.
Co-authored-by: Anukrati Agrawal <anuagra@microsoft.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 6571d0a2-c95e-4c83-8fb7-82debbd8de73
reading declarations
Changes to src/. All files
@@ -1513,8 +1513,8 @@ inline uint32_t constexpr maxCharsPerDigitInRadix(int32_t radix) { // With minNumBitsPerChar being the lower bound estimate of how many bits each // char can represent, the upper bound of how many chars "fit" in a bigint // digit is ceil(sizeofInBits(bigint digit) / minNumBitsPerChar).- uint32_t numCharsPerDigits =- static_cast<uint32_t>(sizeof(uint64_t)) / (1 << minNumBitsPerChar);+ constexpr uint32_t bitsPerDigit = sizeof(uint64_t) * 8;+ uint32_t numCharsPerDigits = (bitsPerDigit + minNumBitsPerChar - 1) / minNumBitsPerChar; return numCharsPerDigits; }@@ -1572,45 +1572,31 @@ jsi::String NodeApiJsiRuntime::bigintToString( // TODO: Add support for big-endian. uint32_t *halfWords = reinterpret_cast<uint32_t *>(words); size_t count = wordCount * 2;- for (size_t i = count; i > 0 && halfWords[i - 1] == 0; --i) {+ while (count > 0 && halfWords[count - 1] == 0) { --count; } uint32_t divisor = static_cast<uint32_t>(radix);- uint32_t remainder = 0; uint64_t word0 = words[0]; do {- // We rewrite the halfWords array as we divide it by radix.+ uint32_t remainder = 0; if (count <= 2) {- remainder = word0 % divisor;- word0 = word0 / divisor;+ remainder = static_cast<uint32_t>(word0 % divisor);+ word0 /= divisor; } else {+ // Divide the whole number in place by radix, from the most significant+ // half-word to the least significant one. for (size_t i = count; i > 0; --i) { uint64_t partialDividend = Make_64(remainder, halfWords[i - 1]);- if (partialDividend == 0) {- halfWords[i] = 0;- remainder = 0;- if (i == count) {- if (--count == 2) {- word0 = words[0];- }- }- } else if (partialDividend < divisor) {- halfWords[i] = 0;- remainder = Lo_32(partialDividend);- if (i == count) {- if (--count == 2) {- word0 = words[0];- }- }- } else if (partialDividend == divisor) {- halfWords[i] = 1;- remainder = 0;- } else {- halfWords[i] = Lo_32(partialDividend / divisor);- remainder = Lo_32(partialDividend % divisor);- }+ halfWords[i - 1] = Lo_32(partialDividend / divisor);+ remainder = Lo_32(partialDividend % divisor);+ }+ while (count > 0 && halfWords[count - 1] == 0) {+ --count;+ }+ if (count <= 2) {+ word0 = words[0]; } }