On Thu, Sep 04, 2025 at 02:55:50PM +0000, [email protected]
wrote:
>> I see that there was some discussion about a Neon implementation upthread,
>> but I'm not sure we concluded anything. For popcount, we first added a
>> Neon version before adding the SVE version, which required more complicated
>> configure/runtime checks. Presumably Neon is available on more hardware
>> than SVE, so that could be a good place to start here, too.
>
> We have added the Neon versions of hex encode/decode.
Thanks. I noticed that this stuff is simple enough that we can use
port/simd.h (with a few added functions). This is especially nice because
it takes care of x86, too. The performance gains look similar to what you
reported for v6:
arm
buf | HEAD | patch | % diff
-------+-------+-------+--------
16 | 13 | 6 | 54
64 | 34 | 9 | 74
256 | 93 | 25 | 73
1024 | 281 | 78 | 72
4096 | 1086 | 227 | 79
16384 | 4382 | 927 | 79
65536 | 17455 | 3608 | 79
x86
buf | HEAD | patch | % diff
-------+-------+-------+--------
16 | 10 | 7 | 30
64 | 29 | 9 | 69
256 | 81 | 21 | 74
1024 | 286 | 66 | 77
4096 | 1106 | 253 | 77
16384 | 4383 | 980 | 78
65536 | 17491 | 3886 | 78
I've only modified hex_encode() for now, but I'm optimistic that we can do
something similar for hex_decode().
--
nathan
>From f2b4f8cf844dead4658469257b771d3394a46ed0 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <[email protected]>
Date: Wed, 10 Sep 2025 21:37:20 -0500
Subject: [PATCH v7 1/1] Optimize hex_encode() using SIMD.
---
src/backend/utils/adt/encode.c | 56 +++++++++++++++-
src/include/port/simd.h | 118 +++++++++++++++++++++++++++++++++
2 files changed, 172 insertions(+), 2 deletions(-)
diff --git a/src/backend/utils/adt/encode.c b/src/backend/utils/adt/encode.c
index 4ccaed815d1..0372d0e787a 100644
--- a/src/backend/utils/adt/encode.c
+++ b/src/backend/utils/adt/encode.c
@@ -16,6 +16,7 @@
#include <ctype.h>
#include "mb/pg_wchar.h"
+#include "port/simd.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
#include "varatt.h"
@@ -177,8 +178,8 @@ static const int8 hexlookup[128] = {
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
};
-uint64
-hex_encode(const char *src, size_t len, char *dst)
+static inline uint64
+hex_encode_scalar(const char *src, size_t len, char *dst)
{
const char *end = src + len;
@@ -193,6 +194,57 @@ hex_encode(const char *src, size_t len, char *dst)
return (uint64) len * 2;
}
+uint64
+hex_encode(const char *src, size_t len, char *dst)
+{
+#ifdef USE_NO_SIMD
+ return hex_encode_scalar(src, len, dst);
+#else
+ const uint64 tail_idx = len & ~(sizeof(Vector8) - 1);
+ uint64 i;
+
+ /*
+ * This works by splitting the high and low nibbles of each byte into
+ * separate vectors, adding the vectors to a mask that converts the
+ * nibbles to their equivalent ASCII bytes, and interleaving those bytes
+ * back together to form the final hex-encoded string. It might be
+ * possible to squeeze out a little more gain by manually unrolling the
+ * loop, but for now we don't bother.
+ */
+ for (i = 0; i < tail_idx; i += sizeof(Vector8))
+ {
+ Vector8 srcv;
+ Vector8 lo;
+ Vector8 hi;
+ Vector8 mask;
+
+ vector8_load(&srcv, (const uint8 *) &src[i]);
+
+ lo = vector8_and(srcv, vector8_broadcast(0x0f));
+ mask = vector8_gt(lo, vector8_broadcast(0x9));
+ mask = vector8_and(mask, vector8_broadcast('a' - '0' - 10));
+ mask = vector8_add(mask, vector8_broadcast('0'));
+ lo = vector8_add(lo, mask);
+
+ hi = vector8_and(srcv, vector8_broadcast(0xf0));
+ hi = vector32_shift_right_nibble((Vector32) hi);
+ mask = vector8_gt(hi, vector8_broadcast(0x9));
+ mask = vector8_and(mask, vector8_broadcast('a' - '0' - 10));
+ mask = vector8_add(mask, vector8_broadcast('0'));
+ hi = vector8_add(hi, mask);
+
+ vector8_store((uint8 *) &dst[i * 2],
+ vector8_interleave_low(hi, lo));
+ vector8_store((uint8 *) &dst[i * 2 + sizeof(Vector8)],
+ vector8_interleave_high(hi, lo));
+ }
+
+ (void) hex_encode_scalar(src + i, len - i, dst + i * 2);
+
+ return (uint64) len * 2;
+#endif
+}
+
static inline bool
get_hex(const char *cp, char *out)
{
diff --git a/src/include/port/simd.h b/src/include/port/simd.h
index 97c5f353022..f1d5353d2b3 100644
--- a/src/include/port/simd.h
+++ b/src/include/port/simd.h
@@ -70,6 +70,7 @@ static inline void vector32_load(Vector32 *v, const uint32
*s);
static inline Vector8 vector8_broadcast(const uint8 c);
#ifndef USE_NO_SIMD
static inline Vector32 vector32_broadcast(const uint32 c);
+static inline void vector8_store(uint8 *s, Vector8 v);
#endif
/* element-wise comparisons to a scalar */
@@ -86,6 +87,8 @@ static inline uint32 vector8_highbit_mask(const Vector8 v);
static inline Vector8 vector8_or(const Vector8 v1, const Vector8 v2);
#ifndef USE_NO_SIMD
static inline Vector32 vector32_or(const Vector32 v1, const Vector32 v2);
+static inline Vector8 vector8_and(const Vector8 v1, const Vector8 v2);
+static inline Vector8 vector8_add(const Vector8 v1, const Vector8 v2);
static inline Vector8 vector8_ssub(const Vector8 v1, const Vector8 v2);
#endif
@@ -99,6 +102,14 @@ static inline Vector8 vector8_ssub(const Vector8 v1, const
Vector8 v2);
static inline Vector8 vector8_eq(const Vector8 v1, const Vector8 v2);
static inline Vector8 vector8_min(const Vector8 v1, const Vector8 v2);
static inline Vector32 vector32_eq(const Vector32 v1, const Vector32 v2);
+static inline Vector8 vector8_gt(const Vector8 v1, const Vector8 v2);
+#endif
+
+/* vector manipulation */
+#ifndef USE_NO_SIMD
+static inline Vector8 vector8_interleave_low(const Vector8 v1, const Vector8
v2);
+static inline Vector8 vector8_interleave_high(const Vector8 v1, const Vector8
v2);
+static inline Vector32 vector32_shift_right_nibble(const Vector32 v1);
#endif
/*
@@ -128,6 +139,21 @@ vector32_load(Vector32 *v, const uint32 *s)
}
#endif /* ! USE_NO_SIMD */
+/*
+ * Store a vector into the given memory address.
+ */
+#ifndef USE_NO_SIMD
+static inline void
+vector8_store(uint8 *s, Vector8 v)
+{
+#ifdef USE_SSE2
+ _mm_storeu_si128((Vector8 *) s, v);
+#elif defined(USE_NEON)
+ vst1q_u8(s, v);
+#endif
+}
+#endif /* ! USE_NO_SIMD */
+
/*
* Create a vector with all elements set to the same value.
*/
@@ -358,6 +384,36 @@ vector32_or(const Vector32 v1, const Vector32 v2)
}
#endif /* ! USE_NO_SIMD */
+/*
+ * Return the bitwise AND of the inputs.
+ */
+#ifndef USE_NO_SIMD
+static inline Vector8
+vector8_and(const Vector8 v1, const Vector8 v2)
+{
+#ifdef USE_SSE2
+ return _mm_and_si128(v1, v2);
+#elif defined(USE_NEON)
+ return vandq_u8(v1, v2);
+#endif
+}
+#endif /* ! USE_NO_SIMD */
+
+/*
+ * Return the result of adding the respective elements of the input vectors.
+ */
+#ifndef USE_NO_SIMD
+static inline Vector8
+vector8_add(const Vector8 v1, const Vector8 v2)
+{
+#ifdef USE_SSE2
+ return _mm_add_epi8(v1, v2);
+#elif defined(USE_NEON)
+ return vaddq_u8(v1, v2);
+#endif
+}
+#endif /* ! USE_NO_SIMD */
+
/*
* Return the result of subtracting the respective elements of the input
* vectors using saturation (i.e., if the operation would yield a value less
@@ -404,6 +460,23 @@ vector32_eq(const Vector32 v1, const Vector32 v2)
}
#endif /* ! USE_NO_SIMD */
+/*
+ * Return a vector with all bits set for each lane of v1 that is greater than
+ * the corresponding lane of v2. NB: The comparison treats the elements as
+ * signed.
+ */
+#ifndef USE_NO_SIMD
+static inline Vector8
+vector8_gt(const Vector8 v1, const Vector8 v2)
+{
+#ifdef USE_SSE2
+ return _mm_cmpgt_epi8(v1, v2);
+#elif defined (USE_NEON)
+ return vcgtq_s8((int8x16_t) v1, (int8x16_t) v2);
+#endif
+}
+#endif /* ! USE_NO_SIMD */
+
/*
* Given two vectors, return a vector with the minimum element of each.
*/
@@ -419,4 +492,49 @@ vector8_min(const Vector8 v1, const Vector8 v2)
}
#endif /* ! USE_NO_SIMD */
+/*
+ * Interleave elements of low halves of given vectors.
+ */
+#ifndef USE_NO_SIMD
+static inline Vector8
+vector8_interleave_low(const Vector8 v1, const Vector8 v2)
+{
+#ifdef USE_SSE2
+ return _mm_unpacklo_epi8(v1, v2);
+#elif defined(USE_NEON)
+ return vzip1q_u8(v1, v2);
+#endif
+}
+#endif /* ! USE_NO_SIMD */
+
+/*
+ * Interleave elements of high halves of given vectors.
+ */
+#ifndef USE_NO_SIMD
+static inline Vector8
+vector8_interleave_high(const Vector8 v1, const Vector8 v2)
+{
+#ifdef USE_SSE2
+ return _mm_unpackhi_epi8(v1, v2);
+#elif defined(USE_NEON)
+ return vzip2q_u8(v1, v2);
+#endif
+}
+#endif /* ! USE_NO_SIMD */
+
+/*
+ * Unsigned shift right of each element in the vector by 4 bits.
+ */
+#ifndef USE_NO_SIMD
+static inline Vector32
+vector32_shift_right_nibble(const Vector32 v1)
+{
+#ifdef USE_SSE2
+ return _mm_srli_epi32(v1, 4);
+#elif defined(USE_NEON)
+ return vshrq_n_u32(v1, 4);
+#endif
+}
+#endif /* ! USE_NO_SIMD */
+
#endif /* SIMD_H */
--
2.39.5 (Apple Git-154)
