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increase BitWriter.write_bits nbits limit, add tests (#1692)

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* increase BitWriter.write_bits nbits limit, add tests

* update releasenotes.md
This commit is contained in:
Denis Palashevskii
2024-12-18 00:21:58 +04:00
committed by GitHub
parent 789b47d565
commit 4839d8861d
3 changed files with 274 additions and 16 deletions
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39
lib/std/io/bits.c3
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@@ -45,6 +45,10 @@ struct BitWriter
uint len;
}
// c3 doesn't allow to shift more than bit width of a variable,
// so use closest byte boundary of 24 instead of 32
const int WRITER_BITS = 24;
fn void BitWriter.init(&self, OutStream byte_writer)
{
*self = { .writer = byte_writer };
@@ -53,7 +57,9 @@ fn void BitWriter.init(&self, OutStream byte_writer)
fn void! BitWriter.flush(&self)
{
if (self.len == 0) return;
uint bits = self.bits << (32 - self.len);
int padding = ($sizeof(self.bits) * 8 - self.len);
uint bits = self.bits << padding;
uint n = (self.len + 7) / 8;
char[4] buffer;
bitorder::write(bits, &buffer, UIntBE);
@@ -62,24 +68,27 @@ fn void! BitWriter.flush(&self)
}
<*
@require nbits <= 8
@require nbits <= 32
*>
fn void! BitWriter.write_bits(&self, uint bits, uint nbits)
{
if (nbits == 0) return;
uint n = self.len + nbits;
uint to_write = n / 8;
uint left = n % 8;
if (to_write > 0)
while (self.len + nbits > WRITER_BITS)
{
ulong lbits;
if (self.len > 0) lbits = (ulong)self.bits << (64 - self.len);
lbits |= (ulong)(bits >> left) << (64 - (n - left));
char[8] buffer;
bitorder::write(lbits, &buffer, ULongBE);
io::write_all(self.writer, buffer[:to_write])!;
uint to_push = WRITER_BITS - self.len;
uint bits_to_push = (bits >> (nbits - to_push)) & ((1 << to_push) - 1);
self.bits <<= to_push;
self.bits |= bits_to_push;
self.len += to_push;
nbits -= to_push;
self.flush()!;
}
self.bits <<= left;
self.bits |= bits & ((1 << left) - 1);
self.len = left;
if (nbits == 0) return;
self.bits <<= nbits;
self.bits |= bits & ((1 << nbits) - 1);
self.len += nbits;
}