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static inline __m128i
enc_translate (const __m128i in)
{
// A lookup table containing the absolute offsets for all ranges:
const __m128i lut = _mm_setr_epi8(
65, 71, -4, -4,
-4, -4, -4, -4,
-4, -4, -4, -4,
-19, -16, 0, 0
);
// Translate values 0..63 to the Base64 alphabet. There are five sets:
// # From To Abs Index Characters
// 0 [0..25] [65..90] +65 0 ABCDEFGHIJKLMNOPQRSTUVWXYZ
// 1 [26..51] [97..122] +71 1 abcdefghijklmnopqrstuvwxyz
// 2 [52..61] [48..57] -4 [2..11] 0123456789
// 3 [62] [43] -19 12 +
// 4 [63] [47] -16 13 /
// Create LUT indices from the input. The index for range #0 is right,
// others are 1 less than expected:
__m128i indices = _mm_subs_epu8(in, _mm_set1_epi8(51));
// mask is 0xFF (-1) for range #[1..4] and 0x00 for range #0:
__m128i mask = _mm_cmpgt_epi8(in, _mm_set1_epi8(25));
// Subtract -1, so add 1 to indices for range #[1..4]. All indices are
// now correct:
indices = _mm_sub_epi8(indices, mask);
// Add offsets to input values:
return _mm_add_epi8(in, _mm_shuffle_epi8(lut, indices));
}
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