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gh-124951: Optimize base64 encode & decode for an easy 2-3x speedup [no SIMD] #143262

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Merged
gpshead merged 13 commits into from
Jan 2, 2026
Merged

gh-124951: Optimize base64 encode & decode for an easy 2-3x speedup [no SIMD] #143262

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2d2be30
Add base64 benchmark tool and optimize encoding/decoding
gpshead Dec 28, 2025
573eaf3
Fix MSVC build: move table_b2a_base64 before inline functions
gpshead Dec 29, 2025
eaac671
NEWS entry
gpshead Dec 29, 2025
060dbf5
Add a whatsnew entry
gpshead Dec 29, 2025
1e12273
expose the benchmark defaults in the help text.
gpshead Dec 29, 2025
ef38895
Align base64 tables to 64-byte cache line boundaries
gpshead Dec 29, 2025
7458c99
Use BASE64_PAD macro instead of literal '=' in fast path
gpshead Dec 29, 2025
1f8ff74
Simplify block comment for base64 helpers
gpshead Dec 29, 2025
4b1245b
Remove binasciibench in favor of pyperformance bm_base64 addition PR.
gpshead Dec 29, 2025
4b50c73
reword L1 cache line comment
gpshead Jan 2, 2026
f7b27ee
doc Contributed by
gpshead Jan 2, 2026
2b13b81
Remove redundant PAD check in base64 decode fast path
gpshead Jan 2, 2026
30976a9
Use pointer increment in base64_encode_fast
gpshead Jan 2, 2026
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Use pointer increment in base64_encode_fast 
Suggested by serhiy-storchaka: replace index math (in + i*3, out + i*4)
with pointer increments. Encode is ~7% faster at 64K (2.11 → 2.25 GB/s).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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@gpshead @claude
gpshead and claude committed Jan 2, 2026
commit 30976a90eb3a6cb5383ced997fd8fd2ab6fa018a
8 changes: 5 additions & 3 deletions Modules/binascii.c
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Original file line number Diff line number Diff line change
Expand Up @@ -134,10 +134,12 @@ base64_encode_fast(const unsigned char *in, Py_ssize_t in_len,
unsigned char *out, const unsigned char *table)
{
Py_ssize_t n_trios = in_len / 3;
Py_ssize_t i;
const unsigned char *in_end = in + n_trios * 3;

for (i = 0; i < n_trios; i++) {
base64_encode_trio(in + i * 3, out + i * 4, table);
while (in < in_end) {
base64_encode_trio(in, out, table);
in += 3;
out += 4;
}

return n_trios * 3;
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