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static inline int
is_nonzero (const uint8x16_t v)
{
uint64_t u64;
const uint64x2_t v64 = vreinterpretq_u64_u8(v);
const uint32x2_t v32 = vqmovn_u64(v64);
vst1_u64(&u64, vreinterpret_u64_u32(v32));
return u64 != 0;
}
static inline uint8x16_t
delta_lookup (const uint8x16_t v)
{
const uint8x8_t lut = {
0, 16, 19, 4, (uint8_t) -65, (uint8_t) -65, (uint8_t) -71, (uint8_t) -71,
};
return vcombine_u8(
vtbl1_u8(lut, vget_low_u8(v)),
vtbl1_u8(lut, vget_high_u8(v)));
}
static inline uint8x16_t
dec_loop_neon32_lane (uint8x16_t *lane)
{
// See the SSSE3 decoder for an explanation of the algorithm.
const uint8x16_t lut_lo = {
0x15, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
0x11, 0x11, 0x13, 0x1A, 0x1B, 0x1B, 0x1B, 0x1A
};
const uint8x16_t lut_hi = {
0x10, 0x10, 0x01, 0x02, 0x04, 0x08, 0x04, 0x08,
0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10
};
const uint8x16_t mask_0F = vdupq_n_u8(0x0F);
const uint8x16_t mask_2F = vdupq_n_u8(0x2F);
const uint8x16_t hi_nibbles = vshrq_n_u8(*lane, 4);
const uint8x16_t lo_nibbles = vandq_u8(*lane, mask_0F);
const uint8x16_t eq_2F = vceqq_u8(*lane, mask_2F);
const uint8x16_t hi = vqtbl1q_u8(lut_hi, hi_nibbles);
const uint8x16_t lo = vqtbl1q_u8(lut_lo, lo_nibbles);
// Now simply add the delta values to the input:
*lane = vaddq_u8(*lane, delta_lookup(vaddq_u8(eq_2F, hi_nibbles)));
// Return the validity mask:
return vandq_u8(lo, hi);
}
static inline void
dec_loop_neon32 (const uint8_t **s, size_t *slen, uint8_t **o, size_t *olen)
{
if (*slen < 64) {
return;
}
// Process blocks of 64 bytes per round. Unlike the SSE codecs, no
// extra trailing zero bytes are written, so it is not necessary to
// reserve extra input bytes:
size_t rounds = *slen / 64;
*slen -= rounds * 64; // 64 bytes consumed per round
*olen += rounds * 48; // 48 bytes produced per round
do {
uint8x16x3_t dec;
// Load 64 bytes and deinterleave:
uint8x16x4_t str = vld4q_u8(*s);
// Decode each lane, collect a mask of invalid inputs:
const uint8x16_t classified
= dec_loop_neon32_lane(&str.val[0])
| dec_loop_neon32_lane(&str.val[1])
| dec_loop_neon32_lane(&str.val[2])
| dec_loop_neon32_lane(&str.val[3]);
// Check for invalid input: if any of the delta values are
// zero, fall back on bytewise code to do error checking and
// reporting:
if (is_nonzero(classified)) {
break;
}
// Compress four bytes into three:
dec.val[0] = vorrq_u8(vshlq_n_u8(str.val[0], 2), vshrq_n_u8(str.val[1], 4));
dec.val[1] = vorrq_u8(vshlq_n_u8(str.val[1], 4), vshrq_n_u8(str.val[2], 2));
dec.val[2] = vorrq_u8(vshlq_n_u8(str.val[2], 6), str.val[3]);
// Interleave and store decoded result:
vst3q_u8(*o, dec);
*s += 64;
*o += 48;
} while (--rounds > 0);
// Adjust for any rounds that were skipped:
*slen += rounds * 64;
*olen -= rounds * 48;
}
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