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Title: gh-124951: Optimize base64 encode & decode for an easy 2-3x speedup [no SIMD] by gpshead · Pull Request #143262 · python/cpython · GitHub

Open Graph Title: gh-124951: Optimize base64 encode & decode for an easy 2-3x speedup [no SIMD] by gpshead · Pull Request #143262 · python/cpython

X Title: gh-124951: Optimize base64 encode & decode for an easy 2-3x speedup [no SIMD] by gpshead · Pull Request #143262 · python/cpython

Description: Optimize base64 encoding/decoding by eliminating loop-carried dependencies. Key changes: Add base64_encode_trio() and base64_decode_quad() helper functions that process complete groups independently Add base64_encode_fast() and base64_decode_fast() wrappers Update b2a_base64 and a2b_base64 to use fast path for complete groups The binasciibench I used measuring base64 encoding/decoding throughput is included in commit history, but i pulled it out of the PR in favor of adding to pyperformance. Performance gains (encode/decode speedup vs main, PGO builds): 64 bytes 64K 1M Zen2: 1.2x/1.8x 1.7x/2.8x 1.5x/2.8x Zen4: 1.2x/1.7x 1.6x/3.0x 1.5x/3.0x [old data, likely faster] M4: 1.3x/1.9x 2.3x/2.8x 2.4x/2.9x [old data, likely faster] RPi5-32: 1.2x/1.2x 2.4x/2.4x 2.0x/2.1x RPi4-64: 1.3x/2.0x 2.4x/5.0x 1.8x/5.0x Additional SIMD implementations (NEON, AVX-512 VBMI) can achieve +50% (M4) to +1500% (!! Zen4) further gains and are planned for follow-on work if deemed simple to maintain. Widely used third party libraries contain industry canonical SIMD accelerated variants such as simdutf (C++ based unfortunately) so the decision of how to link and use those and when is best kept separate. This PR's simple pure better use of modern CPU functional unit pipelining wins make sense regardless. Based on my exploratory work done in main...gpshead:cpython:claude/vectorize-base64-c-S7Hku Issue: gh-124951

Open Graph Description: Optimize base64 encoding/decoding by eliminating loop-carried dependencies. Key changes: Add base64_encode_trio() and base64_decode_quad() helper functions that process complete groups independent...

X Description: Optimize base64 encoding/decoding by eliminating loop-carried dependencies. Key changes: Add base64_encode_trio() and base64_decode_quad() helper functions that process complete groups independent...

Opengraph URL: https://github.com/python/cpython/pull/143262

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2d2be30 Add base64 benchmark tool and optimize encoding/decoding gpshead Dec 28, 2025 https://github.com/python/cpython/pull/143262/commits/2d2be302a54131fe6ad9c02eb91be020e7ca1c42
573eaf3 Fix MSVC build: move table_b2a_base64 before inline functions gpshead Dec 29, 2025 https://github.com/python/cpython/pull/143262/commits/573eaf3fb7d95b44a95225483eab26c09f757b67
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060dbf5 Add a whatsnew entry gpshead Dec 29, 2025 https://github.com/python/cpython/pull/143262/commits/060dbf5ee1ef38214b76c4d42807e1b29dd42c94
1e12273 expose the benchmark defaults in the help text. gpshead Dec 29, 2025 https://github.com/python/cpython/pull/143262/commits/1e12273abe55e73038b283430c38b8832fbcd5c1
ef38895 Align base64 tables to 64-byte cache line boundaries gpshead Dec 29, 2025 https://github.com/python/cpython/pull/143262/commits/ef38895ff3208ed439ba1c63e7a26ea1c77a72ca
7458c99 Use BASE64_PAD macro instead of literal '=' in fast path gpshead Dec 29, 2025 https://github.com/python/cpython/pull/143262/commits/7458c99764b5d590282f126d868c25e11ec0cada
1f8ff74 Simplify block comment for base64 helpers gpshead Dec 29, 2025 https://github.com/python/cpython/pull/143262/commits/1f8ff742672fda7cb6b88689f4be74f985ec6679
4b1245b Remove binasciibench in favor of pyperformance bm_base64 addition PR. gpshead Dec 29, 2025 https://github.com/python/cpython/pull/143262/commits/4b1245be20dcbad0158f2a70fbda7d01c6a59701
4b50c73 reword L1 cache line comment gpshead Jan 2, 2026 https://github.com/python/cpython/pull/143262/commits/4b50c736df0c434f313d0a956e9e97921433e179
f7b27ee doc Contributed by gpshead Jan 2, 2026 https://github.com/python/cpython/pull/143262/commits/f7b27eeb00ed40adbbdc8ae784bfa898cbe4fc2d
2b13b81 Remove redundant PAD check in base64 decode fast path gpshead Jan 2, 2026 https://github.com/python/cpython/pull/143262/commits/2b13b81396a0a6edce4338ad11ad646487c6140d
30976a9 Use pointer increment in base64_encode_fast gpshead Jan 2, 2026 https://github.com/python/cpython/pull/143262/commits/30976a90eb3a6cb5383ced997fd8fd2ab6fa018a
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