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enc_translate.c
57 lines (48 loc) · 2.07 KB
/
enc_translate.c
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static BASE64_FORCE_INLINE uint8x16x4_t
enc_translate (const uint8x16x4_t in)
{
// A lookup table containing the absolute offsets for all ranges:
const uint8x16_t lut = {
65U, 71U, 252U, 252U,
252U, 252U, 252U, 252U,
252U, 252U, 252U, 252U,
237U, 240U, 0U, 0U
};
const uint8x16_t offset = vdupq_n_u8(51);
uint8x16x4_t indices, mask, delta, out;
// 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 input:
// the index for range #0 is right, others are 1 less than expected:
indices.val[0] = vqsubq_u8(in.val[0], offset);
indices.val[1] = vqsubq_u8(in.val[1], offset);
indices.val[2] = vqsubq_u8(in.val[2], offset);
indices.val[3] = vqsubq_u8(in.val[3], offset);
// mask is 0xFF (-1) for range #[1..4] and 0x00 for range #0:
mask.val[0] = vcgtq_u8(in.val[0], vdupq_n_u8(25));
mask.val[1] = vcgtq_u8(in.val[1], vdupq_n_u8(25));
mask.val[2] = vcgtq_u8(in.val[2], vdupq_n_u8(25));
mask.val[3] = vcgtq_u8(in.val[3], vdupq_n_u8(25));
// Subtract -1, so add 1 to indices for range #[1..4], All indices are
// now correct:
indices.val[0] = vsubq_u8(indices.val[0], mask.val[0]);
indices.val[1] = vsubq_u8(indices.val[1], mask.val[1]);
indices.val[2] = vsubq_u8(indices.val[2], mask.val[2]);
indices.val[3] = vsubq_u8(indices.val[3], mask.val[3]);
// Lookup delta values:
delta.val[0] = vqtbl1q_u8(lut, indices.val[0]);
delta.val[1] = vqtbl1q_u8(lut, indices.val[1]);
delta.val[2] = vqtbl1q_u8(lut, indices.val[2]);
delta.val[3] = vqtbl1q_u8(lut, indices.val[3]);
// Add delta values:
out.val[0] = vaddq_u8(in.val[0], delta.val[0]);
out.val[1] = vaddq_u8(in.val[1], delta.val[1]);
out.val[2] = vaddq_u8(in.val[2], delta.val[2]);
out.val[3] = vaddq_u8(in.val[3], delta.val[3]);
return out;
}