Vegard: add link from saidwho12

2022-11-22T08:54:26Z

add link from saidwho12

← Older revision		Revision as of 08:54, 22 November 2022
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	* https://software.intel.com/sites/landingpage/IntrinsicsGuide/		* https://software.intel.com/sites/landingpage/IntrinsicsGuide/
			* https://woboq.com/blog/utf-8-processing-using-simd.html

	[[Category:Programming]]		[[Category:Programming]]

Vegard at 22:33, 14 December 2019

2019-12-14T22:33:12Z

← Older revision		Revision as of 22:33, 14 December 2019
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	[[Category:C]]		[[Category:C]]
	[[Category:C++]]		[[Category:C++]]
			[[Category:x86]]

Vegard: new page

2019-12-14T19:23:28Z

new page

New page

=== Boilerplate ===

<source lang="C">
#include <emmintrin.h>
</source>

=== Get length of string prefix consisting of letters and underscore ===

This can be useful for e.g. parsing identifiers.

The string does not need to be aligned, but beware that up to 15 bytes after the NUL terminator may be loaded from memory, so if these cross a page boundary you can get spurious page faults.

<source lang="C">
int nr_alpha(const char *s)
{
const char *start = s;

__m128i ch_A = _mm_set1_epi8('A' - 1);
__m128i ch_Z = _mm_set1_epi8('Z');
__m128i ch_underscore = _mm_set1_epi8('_');

while (1) {
__m128i ch = _mm_loadu_si128((__m128i *) s);
__m128i b = _mm_and_si128(ch, _mm_set1_epi8(~0x20));
b = _mm_or_si128(_mm_and_si128(_mm_cmpgt_epi8(b, ch_A),
_mm_cmplt_epi8(b, ch_Z)),
_mm_cmpeq_epi8(ch, ch_underscore));

unsigned int ffs = __builtin_ffs(~_mm_movemask_epi8(b)) - 1;
s += ffs;

if (ffs < 16)
return s - start;
}
}
</source>

=== Get length of string prefix consisting of whitespace ===

(See caveats above.)

<source lang="C">
int nr_whitespace(const char *s)
{
const char *start = s;

while (1) {
__m128i ch = _mm_loadu_si128((__m128i *) s);
__m128i b = _mm_or_si128(_mm_cmpeq_epi8(ch, _mm_set1_epi8(' ')),
_mm_cmpeq_epi8(ch, _mm_set1_epi8('\t')));
b = _mm_or_si128(b, _mm_cmpeq_epi8(ch, _mm_set1_epi8('\r')));
b = _mm_or_si128(b, _mm_cmpeq_epi8(ch, _mm_set1_epi8('\n')));

unsigned int ffs = __builtin_ffs(~_mm_movemask_epi8(b)) - 1;
s += ffs;

if (ffs < 16)
return s - start;
}
}
</source>

== See also ==

* https://software.intel.com/sites/landingpage/IntrinsicsGuide/

[[Category:Programming]]
[[Category:C]]
[[Category:C++]]

SSE routines - Revision history

Vegard: add link from saidwho12

Vegard at 22:33, 14 December 2019

Vegard: new page