AuroraMiddleware/qt5base-lts
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Aarch64: vectorize ascii de-/encoding.

Browse Source 
This works only on Aarch64, because the vaddv instruction is only
available on 64bit ARM. Doing something equivalent on 32bit ARM has the
high chance to run into micro-architecture differences: on an Cortex-a8,
transferring a single vector element from NEON to the regular CPU
registers takes 20 cycles(!).

Change-Id: Iccbfe84da82abb9b10f3f3dc35c8b950df69e251
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
This commit is contained in:
Erik Verbruggen 2015-12-03 15:10:47 +01:00 committed by Erik Verbruggen
parent 7c264643f6
commit 923d869b0f
1 changed files with 72 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

73
src/corelib/codecs/qutfcodec.cpp
View File

@ -52,7 +52,8 @@ enum { Endian = 0, Data = 1 };
static const uchar utf8bom[] = { 0xef, 0xbb, 0xbf };
#if defined(__SSE2__) && defined(QT_COMPILER_SUPPORTS_SSE2)
#if (defined(__SSE2__) && defined(QT_COMPILER_SUPPORTS_SSE2)) \
|| (defined(__ARM_NEON__) && defined(Q_PROCESSOR_ARM_64))
static Q_ALWAYS_INLINE uint qBitScanReverse(unsigned v) Q_DECL_NOTHROW
{
uint result = qCountLeadingZeroBits(v);
@ -62,7 +63,9 @@ static Q_ALWAYS_INLINE uint qBitScanReverse(unsigned v) Q_DECL_NOTHROW
result ^= sizeof(unsigned) * 8 - 1;
return result;
}
#endif
#if defined(__SSE2__) && defined(QT_COMPILER_SUPPORTS_SSE2)
static inline bool simdEncodeAscii(uchar *&dst, const ushort *&nextAscii, const ushort *&src, const ushort *end)
{
// do sixteen characters at a time
@ -149,6 +152,74 @@ static inline bool simdDecodeAscii(ushort *&dst, const uchar *&nextAscii, const
}
return src == end;
}
#elif defined(__ARM_NEON__) && defined(Q_PROCESSOR_ARM_64) // vaddv is only available on Aarch64
static inline bool simdEncodeAscii(uchar *&dst, const ushort *&nextAscii, const ushort *&src, const ushort *end)
{
uint16x8_t maxAscii = vdupq_n_u16(0x7f);
uint16x8_t mask1 = { 1, 1 << 2, 1 << 4, 1 << 6, 1 << 8, 1 << 10, 1 << 12, 1 << 14 };
uint16x8_t mask2 = vshlq_n_u16(mask1, 1);
// do sixteen characters at a time
for ( ; end - src >= 16; src += 16, dst += 16) {
// load 2 lanes (or: "load interleaved")
uint16x8x2_t in = vld2q_u16(src);
// check if any of the elements > 0x7f, select 1 bit per element (element 0 -> bit 0, element 1 -> bit 1, etc),
// add those together into a scalar, and merge the scalars.
uint16_t nonAscii = vaddvq_u16(vandq_u16(vcgtq_u16(in.val[0], maxAscii), mask1))
| vaddvq_u16(vandq_u16(vcgtq_u16(in.val[1], maxAscii), mask2));
// merge the two lanes by shifting the values of the second by 8 and inserting them
uint16x8_t out = vsliq_n_u16(in.val[0], in.val[1], 8);
// store, even if there are non-ASCII characters here
vst1q_u8(dst, vreinterpretq_u8_u16(out));
if (nonAscii) {
// find the next probable ASCII character
// we don't want to load 32 bytes again in this loop if we know there are non-ASCII
// characters still coming
nextAscii = src + qBitScanReverse(nonAscii) + 1;
nonAscii = qCountTrailingZeroBits(nonAscii);
dst += nonAscii;
src += nonAscii;
return false;
}
}
return src == end;
}
static inline bool simdDecodeAscii(ushort *&dst, const uchar *&nextAscii, const uchar *&src, const uchar *end)
{
// do eight characters at a time
uint8x8_t msb_mask = vdup_n_u8(0x80);
uint8x8_t add_mask = { 1, 1 << 1, 1 << 2, 1 << 3, 1 << 4, 1 << 5, 1 << 6, 1 << 7 };
for ( ; end - src >= 8; src += 8, dst += 8) {
uint8x8_t c = vld1_u8(src);
uint8_t n = vaddv_u8(vand_u8(vcge_u8(c, msb_mask), add_mask));
if (!n) {
// store
vst1q_u16(dst, vmovl_u8(c));
continue;
}
// copy the front part that is still ASCII
while (!(n & 1)) {
*dst++ = *src++;
n >>= 1;
}
// find the next probable ASCII character
// we don't want to load 16 bytes again in this loop if we know there are non-ASCII
// characters still coming
n = qBitScanReverse(n);
nextAscii = src + n + 1;
return false;
}
return src == end;
}
#else
static inline bool simdEncodeAscii(uchar *, const ushort *, const ushort *, const ushort *)
{