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dec_loop.c
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dec_loop.c
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// 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
//
// We will use lookup tables for character validation and offset computation.
// Remember that 0x2X and 0x0X are the same index for _mm_shuffle_epi8, this
// allows to mask with 0x2F instead of 0x0F and thus save one constant
// declaration (register and/or memory access).
//
// For offsets:
// Perfect hash for lut = ((src >> 4) & 0x2F) + ((src == 0x2F) ? 0xFF : 0x00)
// 0000 = garbage
// 0001 = /
// 0010 = +
// 0011 = 0-9
// 0100 = A-Z
// 0101 = A-Z
// 0110 = a-z
// 0111 = a-z
// 1000 >= garbage
//
// For validation, here's the table.
// A character is valid if and only if the AND of the 2 lookups equals 0:
//
// hi \ lo 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111
// LUT 0x15 0x11 0x11 0x11 0x11 0x11 0x11 0x11 0x11 0x11 0x13 0x1A 0x1B 0x1B 0x1B 0x1A
//
// 0000 0x10 char NUL SOH STX ETX EOT ENQ ACK BEL BS HT LF VT FF CR SO SI
// andlut 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10
//
// 0001 0x10 char DLE DC1 DC2 DC3 DC4 NAK SYN ETB CAN EM SUB ESC FS GS RS US
// andlut 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10
//
// 0010 0x01 char ! " # $ % & ' ( ) * + , - . /
// andlut 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x00 0x01 0x01 0x01 0x00
//
// 0011 0x02 char 0 1 2 3 4 5 6 7 8 9 : ; < = > ?
// andlut 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x02 0x02 0x02 0x02 0x02 0x02
//
// 0100 0x04 char @ A B C D E F G H I J K L M N O
// andlut 0x04 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
//
// 0101 0x08 char P Q R S T U V W X Y Z [ \ ] ^ _
// andlut 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x08 0x08 0x08 0x08 0x08
//
// 0110 0x04 char ` a b c d e f g h i j k l m n o
// andlut 0x04 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
// 0111 0x08 char p q r s t u v w x y z { | } ~
// andlut 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x08 0x08 0x08 0x08 0x08
//
// 1000 0x10 andlut 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10
// 1001 0x10 andlut 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10
// 1010 0x10 andlut 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10
// 1011 0x10 andlut 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10
// 1100 0x10 andlut 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10
// 1101 0x10 andlut 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10
// 1110 0x10 andlut 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10
// 1111 0x10 andlut 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10 0x10
static BASE64_FORCE_INLINE int
dec_loop_ssse3_inner (const uint8_t **s, uint8_t **o, size_t *rounds)
{
const __m128i lut_lo = _mm_setr_epi8(
0x15, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
0x11, 0x11, 0x13, 0x1A, 0x1B, 0x1B, 0x1B, 0x1A);
const __m128i lut_hi = _mm_setr_epi8(
0x10, 0x10, 0x01, 0x02, 0x04, 0x08, 0x04, 0x08,
0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10);
const __m128i lut_roll = _mm_setr_epi8(
0, 16, 19, 4, -65, -65, -71, -71,
0, 0, 0, 0, 0, 0, 0, 0);
const __m128i mask_2F = _mm_set1_epi8(0x2F);
// Load input:
__m128i str = _mm_loadu_si128((__m128i *) *s);
// Table lookups:
const __m128i hi_nibbles = _mm_and_si128(_mm_srli_epi32(str, 4), mask_2F);
const __m128i lo_nibbles = _mm_and_si128(str, mask_2F);
const __m128i hi = _mm_shuffle_epi8(lut_hi, hi_nibbles);
const __m128i lo = _mm_shuffle_epi8(lut_lo, lo_nibbles);
// Check for invalid input: if any "and" values from lo and hi are not
// zero, fall back on bytewise code to do error checking and reporting:
if (_mm_movemask_epi8(_mm_cmpgt_epi8(_mm_and_si128(lo, hi), _mm_setzero_si128())) != 0) {
return 0;
}
const __m128i eq_2F = _mm_cmpeq_epi8(str, mask_2F);
const __m128i roll = _mm_shuffle_epi8(lut_roll, _mm_add_epi8(eq_2F, hi_nibbles));
// Now simply add the delta values to the input:
str = _mm_add_epi8(str, roll);
// Reshuffle the input to packed 12-byte output format:
str = dec_reshuffle(str);
// Store the output:
_mm_storeu_si128((__m128i *) *o, str);
*s += 16;
*o += 12;
*rounds -= 1;
return 1;
}
static inline void
dec_loop_ssse3 (const uint8_t **s, size_t *slen, uint8_t **o, size_t *olen)
{
if (*slen < 24) {
return;
}
// Process blocks of 16 bytes per round. Because 4 extra zero bytes are
// written after the output, ensure that there will be at least 8 bytes
// of input data left to cover the gap. (6 data bytes and up to two
// end-of-string markers.)
size_t rounds = (*slen - 8) / 16;
*slen -= rounds * 16; // 16 bytes consumed per round
*olen += rounds * 12; // 12 bytes produced per round
do {
if (rounds >= 8) {
if (dec_loop_ssse3_inner(s, o, &rounds) &&
dec_loop_ssse3_inner(s, o, &rounds) &&
dec_loop_ssse3_inner(s, o, &rounds) &&
dec_loop_ssse3_inner(s, o, &rounds) &&
dec_loop_ssse3_inner(s, o, &rounds) &&
dec_loop_ssse3_inner(s, o, &rounds) &&
dec_loop_ssse3_inner(s, o, &rounds) &&
dec_loop_ssse3_inner(s, o, &rounds)) {
continue;
}
break;
}
if (rounds >= 4) {
if (dec_loop_ssse3_inner(s, o, &rounds) &&
dec_loop_ssse3_inner(s, o, &rounds) &&
dec_loop_ssse3_inner(s, o, &rounds) &&
dec_loop_ssse3_inner(s, o, &rounds)) {
continue;
}
break;
}
if (rounds >= 2) {
if (dec_loop_ssse3_inner(s, o, &rounds) &&
dec_loop_ssse3_inner(s, o, &rounds)) {
continue;
}
break;
}
dec_loop_ssse3_inner(s, o, &rounds);
break;
} while (rounds > 0);
// Adjust for any rounds that were skipped:
*slen += rounds * 16;
*olen -= rounds * 12;
}