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// If we have AVX2 support, pick off 32 bytes at a time for as long as we can,
// but make sure that we quit before seeing any == markers at the end of the
// string. Also, because we write 8 zeroes at the end of the output, ensure
// that there are at least 11 valid bytes of input data remaining to close the
// gap. 32 + 2 + 11 = 45 bytes:
while (srclen >= 45)
{
// Load string:
__m256i str = _mm256_loadu_si256((__m256i *)c);
// The input consists of six character sets in the Base64 alphabet,
// which we need to map back to the 6-bit values they represent.
// There are three ranges, two singles, and then there's the rest.
//
// # From To Add Characters
// 1 [43] [62] +19 +
// 2 [47] [63] +16 /
// 3 [48..57] [52..61] +4 0..9
// 4 [65..90] [0..25] -65 A..Z
// 5 [97..122] [26..51] -71 a..z
// (6) Everything else => invalid input
const __m256i set1 = CMPEQ(str, '+');
const __m256i set2 = CMPEQ(str, '/');
const __m256i set3 = RANGE(str, '0', '9');
const __m256i set4 = RANGE(str, 'A', 'Z');
const __m256i set5 = RANGE(str, 'a', 'z');
const __m256i set6 = CMPEQ(str, '-');
const __m256i set7 = CMPEQ(str, '_');
__m256i delta = REPLACE(set1, 19);
delta = _mm256_or_si256(delta, REPLACE(set2, 16));
delta = _mm256_or_si256(delta, REPLACE(set3, 4));
delta = _mm256_or_si256(delta, REPLACE(set4, -65));
delta = _mm256_or_si256(delta, REPLACE(set5, -71));
delta = _mm256_or_si256(delta, REPLACE(set6, 17));
delta = _mm256_or_si256(delta, REPLACE(set7, -32));
// Check for invalid input: if any of the delta values are zero,
// fall back on bytewise code to do error checking and reporting:
#ifdef _MSC_VER
// Hack for MSVC miscompilation - it inserts vzeroupper for the break
// (we need to clear YMM registers before exiting the function)
// while delta and str are still in the registers.
// Save delta/str in memory manually.
_mm256_zeroupper();
#endif
if (_mm256_movemask_epi8(CMPEQ(delta, 0))) {
break;
}
// Now simply add the delta values to the input:
str = _mm256_add_epi8(str, delta);
// Reshuffle the input to packed 12-byte output format:
str = dec_reshuffle(str);
// Store back:
_mm256_storeu_si256((__m256i *)o, str);
c += 32;
o += 24;
outl += 24;
srclen -= 32;
}
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