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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
+134 −23
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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Fix MSVC build: move table_b2a_base64 before inline functions 
MSVC doesn't support forward declarations of arrays without explicit
size. Move the table definition before the inline functions that use
it, eliminating the need for a forward declaration.

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
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@gpshead @claude
gpshead and claude committed Dec 29, 2025
commit 573eaf3fb7d95b44a95225483eab26c09f757b67
7 changes: 2 additions & 5 deletions Modules/binascii.c
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Original file line number Diff line number Diff line change
Expand Up @@ -109,8 +109,8 @@ static const unsigned char table_a2b_base64[] = {
* This allows the compiler to better optimize the hot loops.
*/

/* Forward declaration for table defined after the inline functions */
static const unsigned char table_b2a_base64[];
static const unsigned char table_b2a_base64[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

/* Encode 3 bytes into 4 base64 characters. */
static inline void
Expand Down Expand Up @@ -198,9 +198,6 @@ base64_decode_fast(const unsigned char *in, Py_ssize_t in_len,
return i * 4;
}

static const unsigned char table_b2a_base64[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";


static const unsigned short crctab_hqx[256] = {
0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
Expand Down
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