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Merge ef24fee305 into 82d322c497

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AGSaidi 2026-08-03 13:24:24 +03:00 • committed by GitHub
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1 changed files with 31 additions and 20 deletions
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51
lib/compress/hist.c
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@ -74,6 +74,17 @@ typedef enum { trustInput, checkMaxSymbolValue } HIST_checkInput_e;
#if defined(ZSTD_ARCH_ARM_SVE2)
FORCE_INLINE_TEMPLATE size_t min_size(size_t a, size_t b) { return a < b ? a : b; }
/* Saturating widen-add of 8-bit histogram partials into 16-bit accumulators.
* A 16-bit accumulator can only represent 65535, but HIST_count runs on blocks
* up to ZSTD_BLOCKSIZE_MAX (128 KB), so a symbol occurring >65535 times in a
* block would wrap a plain svaddwb/svaddwt to a small value, making a frequent
* symbol look rare and producing a bad (but still valid) Huffman table.
* Saturating at 65535 preserves the frequency ordering, so the table is
* essentially unchanged. The extra widen only runs in the per-240-byte
* reduction, not the inner svhistseg loop. */
#define HIST_ADDWB_SAT(acc, h) svqadd_u16((acc), svshllb_n_u16((h), 0))
#define HIST_ADDWT_SAT(acc, h) svqadd_u16((acc), svshllt_n_u16((h), 0))
static
svuint16_t HIST_count_6_sve2(const BYTE* const src, size_t size, U32* const dst,
const svuint8_t c0, const svuint8_t c1,
@ -121,18 +132,18 @@ svuint16_t HIST_count_6_sve2(const BYTE* const src, size_t size, U32* const dst,
h5 = svadd_u8_x(vl128, h5, svhistseg_u8(c5, c));
}
hh0 = svaddwb_u16(hh0, h0);
hh1 = svaddwt_u16(hh1, h0);
hh2 = svaddwb_u16(hh2, h1);
hh3 = svaddwt_u16(hh3, h1);
hh4 = svaddwb_u16(hh4, h2);
hh5 = svaddwt_u16(hh5, h2);
hh6 = svaddwb_u16(hh6, h3);
hh7 = svaddwt_u16(hh7, h3);
hh8 = svaddwb_u16(hh8, h4);
hh9 = svaddwt_u16(hh9, h4);
hha = svaddwb_u16(hha, h5);
hhb = svaddwt_u16(hhb, h5);
hh0 = HIST_ADDWB_SAT(hh0, h0);
hh1 = HIST_ADDWT_SAT(hh1, h0);
hh2 = HIST_ADDWB_SAT(hh2, h1);
hh3 = HIST_ADDWT_SAT(hh3, h1);
hh4 = HIST_ADDWB_SAT(hh4, h2);
hh5 = HIST_ADDWT_SAT(hh5, h2);
hh6 = HIST_ADDWB_SAT(hh6, h3);
hh7 = HIST_ADDWT_SAT(hh7, h3);
hh8 = HIST_ADDWB_SAT(hh8, h4);
hh9 = HIST_ADDWT_SAT(hh9, h4);
hha = HIST_ADDWB_SAT(hha, h5);
hhb = HIST_ADDWT_SAT(hhb, h5);
}
svst1_u32(svwhilelt_b32_u64( 0, maxCount), dst + 0, svshllb_n_u32(hh0, 0));
@ -230,14 +241,14 @@ static size_t HIST_count_sve2(unsigned* count, unsigned* maxSymbolValuePtr,
symbolMax = svmax_u8_x(vl128, symbolMax, c);
}
hh0 = svaddwb_u16(hh0, h0);
hh1 = svaddwt_u16(hh1, h0);
hh2 = svaddwb_u16(hh2, h1);
hh3 = svaddwt_u16(hh3, h1);
hh4 = svaddwb_u16(hh4, h2);
hh5 = svaddwt_u16(hh5, h2);
hh6 = svaddwb_u16(hh6, h3);
hh7 = svaddwt_u16(hh7, h3);
hh0 = HIST_ADDWB_SAT(hh0, h0);
hh1 = HIST_ADDWT_SAT(hh1, h0);
hh2 = HIST_ADDWB_SAT(hh2, h1);
hh3 = HIST_ADDWT_SAT(hh3, h1);
hh4 = HIST_ADDWB_SAT(hh4, h2);
hh5 = HIST_ADDWT_SAT(hh5, h2);
hh6 = HIST_ADDWB_SAT(hh6, h3);
hh7 = HIST_ADDWT_SAT(hh7, h3);
}
maxSymbolValue = svmaxv_u8(vl128, symbolMax);