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130 lines
5.1 KiB
C
130 lines
5.1 KiB
C
// The input consists of five valid character sets in the Base64 alphabet,
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// which we need to map back to the 6-bit values they represent.
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// There are three ranges, two singles, and then there's the rest.
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//
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// # From To LUT Characters
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// 1 [0..42] [255] #1 invalid input
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// 2 [43] [62] #1 +
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// 3 [44..46] [255] #1 invalid input
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// 4 [47] [63] #1 /
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// 5 [48..57] [52..61] #1 0..9
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// 6 [58..63] [255] #1 invalid input
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// 7 [64] [255] #2 invalid input
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// 8 [65..90] [0..25] #2 A..Z
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// 9 [91..96] [255] #2 invalid input
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// 10 [97..122] [26..51] #2 a..z
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// 11 [123..126] [255] #2 invalid input
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// (12) Everything else => invalid input
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// The first LUT will use the VTBL instruction (out of range indices are set to
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// 0 in destination).
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static const uint8_t dec_lut1[] = {
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255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U,
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255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U,
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255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 62U, 255U, 255U, 255U, 63U,
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52U, 53U, 54U, 55U, 56U, 57U, 58U, 59U, 60U, 61U, 255U, 255U, 255U, 255U, 255U, 255U,
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};
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// The second LUT will use the VTBX instruction (out of range indices will be
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// unchanged in destination). Input [64..126] will be mapped to index [1..63]
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// in this LUT. Index 0 means that value comes from LUT #1.
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static const uint8_t dec_lut2[] = {
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0U, 255U, 0U, 1U, 2U, 3U, 4U, 5U, 6U, 7U, 8U, 9U, 10U, 11U, 12U, 13U,
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14U, 15U, 16U, 17U, 18U, 19U, 20U, 21U, 22U, 23U, 24U, 25U, 255U, 255U, 255U, 255U,
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255U, 255U, 26U, 27U, 28U, 29U, 30U, 31U, 32U, 33U, 34U, 35U, 36U, 37U, 38U, 39U,
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40U, 41U, 42U, 43U, 44U, 45U, 46U, 47U, 48U, 49U, 50U, 51U, 255U, 255U, 255U, 255U,
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};
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// All input values in range for the first look-up will be 0U in the second
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// look-up result. All input values out of range for the first look-up will be
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// 0U in the first look-up result. Thus, the two results can be ORed without
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// conflicts.
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//
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// Invalid characters that are in the valid range for either look-up will be
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// set to 255U in the combined result. Other invalid characters will just be
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// passed through with the second look-up result (using the VTBX instruction).
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// Since the second LUT is 64 bytes, those passed-through values are guaranteed
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// to have a value greater than 63U. Therefore, valid characters will be mapped
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// to the valid [0..63] range and all invalid characters will be mapped to
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// values greater than 63.
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static inline void
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dec_loop_neon64 (const uint8_t **s, size_t *slen, uint8_t **o, size_t *olen)
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{
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if (*slen < 64) {
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return;
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}
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// Process blocks of 64 bytes per round. Unlike the SSE codecs, no
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// extra trailing zero bytes are written, so it is not necessary to
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// reserve extra input bytes:
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size_t rounds = *slen / 64;
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*slen -= rounds * 64; // 64 bytes consumed per round
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*olen += rounds * 48; // 48 bytes produced per round
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const uint8x16x4_t tbl_dec1 = load_64byte_table(dec_lut1);
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const uint8x16x4_t tbl_dec2 = load_64byte_table(dec_lut2);
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do {
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const uint8x16_t offset = vdupq_n_u8(63U);
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uint8x16x4_t dec1, dec2;
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uint8x16x3_t dec;
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// Load 64 bytes and deinterleave:
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uint8x16x4_t str = vld4q_u8((uint8_t *) *s);
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// Get indices for second LUT:
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dec2.val[0] = vqsubq_u8(str.val[0], offset);
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dec2.val[1] = vqsubq_u8(str.val[1], offset);
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dec2.val[2] = vqsubq_u8(str.val[2], offset);
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dec2.val[3] = vqsubq_u8(str.val[3], offset);
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// Get values from first LUT:
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dec1.val[0] = vqtbl4q_u8(tbl_dec1, str.val[0]);
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dec1.val[1] = vqtbl4q_u8(tbl_dec1, str.val[1]);
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dec1.val[2] = vqtbl4q_u8(tbl_dec1, str.val[2]);
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dec1.val[3] = vqtbl4q_u8(tbl_dec1, str.val[3]);
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// Get values from second LUT:
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dec2.val[0] = vqtbx4q_u8(dec2.val[0], tbl_dec2, dec2.val[0]);
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dec2.val[1] = vqtbx4q_u8(dec2.val[1], tbl_dec2, dec2.val[1]);
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dec2.val[2] = vqtbx4q_u8(dec2.val[2], tbl_dec2, dec2.val[2]);
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dec2.val[3] = vqtbx4q_u8(dec2.val[3], tbl_dec2, dec2.val[3]);
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// Get final values:
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str.val[0] = vorrq_u8(dec1.val[0], dec2.val[0]);
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str.val[1] = vorrq_u8(dec1.val[1], dec2.val[1]);
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str.val[2] = vorrq_u8(dec1.val[2], dec2.val[2]);
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str.val[3] = vorrq_u8(dec1.val[3], dec2.val[3]);
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// Check for invalid input, any value larger than 63:
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const uint8x16_t classified
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= vcgtq_u8(str.val[0], vdupq_n_u8(63))
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| vcgtq_u8(str.val[1], vdupq_n_u8(63))
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| vcgtq_u8(str.val[2], vdupq_n_u8(63))
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| vcgtq_u8(str.val[3], vdupq_n_u8(63));
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// Check that all bits are zero:
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if (vmaxvq_u8(classified) != 0U) {
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break;
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}
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// Compress four bytes into three:
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dec.val[0] = vshlq_n_u8(str.val[0], 2) | vshrq_n_u8(str.val[1], 4);
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dec.val[1] = vshlq_n_u8(str.val[1], 4) | vshrq_n_u8(str.val[2], 2);
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dec.val[2] = vshlq_n_u8(str.val[2], 6) | str.val[3];
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// Interleave and store decoded result:
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vst3q_u8((uint8_t *) *o, dec);
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*s += 64;
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*o += 48;
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} while (--rounds > 0);
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// Adjust for any rounds that were skipped:
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*slen += rounds * 64;
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*olen -= rounds * 48;
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}
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