Compiler Explorer

Source code

// SPDX-License-Identifier: 0BSD OR MIT-0

#include <stdint.h>
#include <immintrin.h>

static inline __m512i
tolower64(__m512i c) {
        __m512i A = _mm512_set1_epi8('A');
        __m512i Z = _mm512_set1_epi8('Z');
        __m512i to_upper = _mm512_set1_epi8('a' - 'A');
        __mmask64 ge_A = _mm512_cmpge_epi8_mask(c, A);
        __mmask64 le_Z = _mm512_cmple_epi8_mask(c, Z);
        __mmask64 is_upper = _kand_mask64(ge_A, le_Z);
        return  _mm512_mask_add_epi8(c, is_upper, c, to_upper);
}

void *
copytolower64(void *restrict vdst, const void *restrict vsrc, size_t len) {
        const uint8_t *src = vsrc;
        uint8_t *dst = vdst;
        while (len >= sizeof(__m512i)) {
                __m512i src_v = _mm512_loadu_epi8(src);
                __m512i dst_v = tolower64(src_v);
                _mm512_storeu_epi8(dst, dst_v);
                dst += sizeof(__m512i);
                src += sizeof(__m512i);
                len -= sizeof(__m512i);
        }
        if (len > 0) {
                uint64_t len_bits = (~0ULL) >> (64 - len);
                __mmask64 len_mask =  _cvtu64_mask64(len_bits);
                __m512i src_v = _mm512_maskz_loadu_epi8(len_mask, src);
                __m512i dst_v = tolower64(src_v);
                _mm512_mask_storeu_epi8(dst, len_mask, dst_v);
        }
        return(vdst);
}