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base/memset: speedup implementation

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Compared to the bytewise memset, a wordwise memset (or even multi-word)
achieves a speedup of ~6.

On Zynq-7000/Cortex-A9:
317 MiB/s -> 2040 MiB/s

On base-linux x86_64:
3580 MiB/s -> 23700 MiB/s

genodelabs/genode#4456
This commit is contained in:
Johannes Schlatow 2022-03-25 11:52:20 +01:00 committed by Christian Helmuth
parent 9409f814a4
commit 410099df70
1 changed files with 41 additions and 1 deletions
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42
repos/base/include/util/string.h
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@ -246,7 +246,47 @@ namespace Genode {
__attribute((optimize("no-tree-loop-distribute-patterns")))
inline void *memset(void *dst, uint8_t i, size_t size)
{
while (size--) ((uint8_t *)dst)[size] = i;
typedef unsigned long word_t;
enum {
LEN = sizeof(word_t),
MASK = LEN-1
};
size_t d_align = (size_t)dst & MASK;
uint8_t* d = (uint8_t*)dst;
/* write until word aligned */
for (; d_align && d_align < LEN && size;
d_align++, size--, d++)
*d = i;
word_t word = i;
word |= word << 8;
word |= word << 16;
if (LEN == 8)
word |= (word << 16) << 16;
/* write 8-word chunks (likely matches cache line size) */
for (; size >= 8*LEN; size -= 8*LEN, d += 8*LEN) {
((word_t *)d)[0] = word;
((word_t *)d)[1] = word;
((word_t *)d)[2] = word;
((word_t *)d)[3] = word;
((word_t *)d)[4] = word;
((word_t *)d)[5] = word;
((word_t *)d)[6] = word;
((word_t *)d)[7] = word;
}
/* write remaining words */
for (; size >= LEN; size -= LEN, d += LEN)
((word_t *)d)[0] = word;
/* write remaining bytes */
for (; size; size--, d++)
*d = i;
return dst;
}