Date: Mon, 22 Sep 2025 15:05:44 -0500
From: Nathan Bossart <nathandbossart@gmail.com>
To: "Chiranmoy.Bhattacharya@fujitsu.com" <Chiranmoy.Bhattacharya@fujitsu.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, John Naylor <johncnaylorls@gmail.com>,
	David Rowley <dgrowleyml@gmail.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>,
	"Devanga.Susmitha@fujitsu.com" <Devanga.Susmitha@fujitsu.com>,
	"Ragesh.Hajela@fujitsu.com" <Ragesh.Hajela@fujitsu.com>
Subject: Re: [PATCH] Hex-coding optimizations using SVE on ARM.
Message-ID: <aNGsGMowsTwd5_aY@nathan>
References: 
 <OS9PR01MB15185626CA7C6EAF82C93ABA3974FA@OS9PR01MB15185.jpnprd01.prod.outlook.com>
 <TY4PR01MB15177710A7DF163A8536F26289701A@TY4PR01MB15177.jpnprd01.prod.outlook.com>
 <CANWCAZZm4zwAFmy6M32Sj2BfDg8ZjEV4TJ0YwBQewjV=AUY1Qw@mail.gmail.com>
 <OS9PR01MB15185B278E343A9BA5F0F6AB19700A@OS9PR01MB15185.jpnprd01.prod.outlook.com>
 <aMI-NF6KLc1x1pko@nathan>
 <OS9PR01MB1518513BA12A54A243342A2999709A@OS9PR01MB15185.jpnprd01.prod.outlook.com>
 <aMLpq9_wOz_tnHmm@nathan>
 <1787140.1757604720@sss.pgh.pa.us>
 <OS9PR01MB1518531C5857F194371EBCA329708A@OS9PR01MB15185.jpnprd01.prod.outlook.com>
 <aMSQ7ackQO-P7T3S@nathan>
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On Fri, Sep 12, 2025 at 04:30:21PM -0500, Nathan Bossart wrote:
> I've attached a new version of the patch with a simd.h version of
> hex_decode().  Here are the numbers:

I was able to improve the hex_decode() implementation a bit.

                arm
    buf  | HEAD  | patch | % diff
  -------+-------+-------+--------
      16 |    11 |    11 |    0
      64 |    38 |     7 |   82
     256 |   133 |    18 |   86
    1024 |   513 |    67 |   87
    4096 |  2037 |   271 |   87
   16384 |  8326 |  1103 |   87
   65536 | 34550 |  4475 |   87

                x86
    buf  | HEAD  | patch | % diff
  -------+-------+-------+--------
      16 |     8 |     9 |  -13
      64 |    38 |     7 |   82
     256 |   121 |    24 |   80
    1024 |   457 |    91 |   80
    4096 |  1797 |   356 |   80
   16384 |  7161 |  1411 |   80
   65536 | 28620 |  5632 |   80

-- 
nathan

--1egPQYR2VaA9f9J/
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename=v10-0001-Optimize-hex_encode-and-hex_decode-using-SIMD.patch

From ba097b763eb80ab8c9c78503fcb5be5575342ff8 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Fri, 12 Sep 2025 15:51:55 -0500
Subject: [PATCH v10 1/1] Optimize hex_encode() and hex_decode() using SIMD.

---
 src/backend/utils/adt/encode.c | 131 ++++++++++++++++++-
 src/include/port/simd.h        | 227 ++++++++++++++++++++++++++++++++-
 2 files changed, 348 insertions(+), 10 deletions(-)

diff --git a/src/backend/utils/adt/encode.c b/src/backend/utils/adt/encode.c
index 9a9c7e8da99..028e0ca6887 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(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)
 {
@@ -213,8 +265,8 @@ hex_decode(const char *src, size_t len, char *dst)
 	return hex_decode_safe(src, len, dst, NULL);
 }
 
-uint64
-hex_decode_safe(const char *src, size_t len, char *dst, Node *escontext)
+static inline uint64
+hex_decode_safe_scalar(const char *src, size_t len, char *dst, Node *escontext)
 {
 	const char *s,
 			   *srcend;
@@ -254,6 +306,77 @@ hex_decode_safe(const char *src, size_t len, char *dst, Node *escontext)
 	return p - dst;
 }
 
+/*
+ * This helper converts each byte to its binary-equivalent nibble by
+ * subtraction and combines them to form the return bytes (separated by zero
+ * bytes).  Returns false if any input bytes are outside the expected ranges of
+ * ASCII values.  Otherwise, returns true.
+ */
+#ifndef USE_NO_SIMD
+static inline bool
+hex_decode_simd_helper(const Vector8 src, Vector8 *dst)
+{
+	Vector8		sub;
+	Vector8		msk;
+
+	msk = vector8_gt(vector8_broadcast('9' + 1), src);
+	sub = vector8_and(msk, vector8_broadcast('0'));
+
+	msk = vector8_gt(src, vector8_broadcast('A' - 1));
+	msk = vector8_and(msk, vector8_broadcast('A' - 10));
+	sub = vector8_add(sub, msk);
+
+	msk = vector8_gt(src, vector8_broadcast('a' - 1));
+	msk = vector8_and(msk, vector8_broadcast('a' - 'A'));
+	sub = vector8_add(sub, msk);
+
+	*dst = vector8_sssub(src, sub);
+	if (unlikely(vector8_has_ge(*dst, 0x10)))
+		return false;
+
+	msk = vector8_and(*dst, vector32_broadcast(0xff00ff00));
+	msk = vector32_shift_right_byte(msk);
+	*dst = vector8_and(*dst, vector32_broadcast(0x00ff00ff));
+	*dst = vector32_shift_left_nibble(*dst);
+	*dst = vector8_or(*dst, msk);
+	return true;
+}
+#endif							/* ! USE_NO_SIMD */
+
+uint64
+hex_decode_safe(const char *src, size_t len, char *dst, Node *escontext)
+{
+#ifdef USE_NO_SIMD
+	return hex_decode_safe_scalar(src, len, dst, escontext);
+#else
+	const uint64 tail_idx = len & ~(sizeof(Vector8) * 2 - 1);
+	uint64		i;
+
+	/*
+	 * We must process 2 vectors at a time since the output will be half the
+	 * length of the input.
+	 */
+	for (i = 0; i < tail_idx; i += sizeof(Vector8) * 2)
+	{
+		Vector8		srcv;
+		Vector8		dstv1;
+		Vector8		dstv2;
+
+		vector8_load(&srcv, (const uint8 *) &src[i]);
+		if (unlikely(!hex_decode_simd_helper(srcv, &dstv1)))
+			break;
+
+		vector8_load(&srcv, (const uint8 *) &src[i + sizeof(Vector8)]);
+		if (unlikely(!hex_decode_simd_helper(srcv, &dstv2)))
+			break;
+
+		vector8_store((uint8 *) &dst[i / 2], vector8_pack_16(dstv1, dstv2));
+	}
+
+	return i / 2 + hex_decode_safe_scalar(src + i, len - i, dst + i / 2, escontext);
+#endif
+}
+
 static uint64
 hex_enc_len(const char *src, size_t srclen)
 {
diff --git a/src/include/port/simd.h b/src/include/port/simd.h
index 97c5f353022..8059e37acc7 100644
--- a/src/include/port/simd.h
+++ b/src/include/port/simd.h
@@ -70,12 +70,16 @@ 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 */
 static inline bool vector8_has(const Vector8 v, const uint8 c);
 static inline bool vector8_has_zero(const Vector8 v);
 static inline bool vector8_has_le(const Vector8 v, const uint8 c);
+#ifndef USE_NO_SIMD
+static inline bool vector8_has_ge(const Vector8 v, const uint8 c);
+#endif
 static inline bool vector8_is_highbit_set(const Vector8 v);
 #ifndef USE_NO_SIMD
 static inline bool vector32_is_highbit_set(const Vector32 v);
@@ -86,7 +90,10 @@ 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_ssub(const Vector8 v1, const Vector8 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_sssub(const Vector8 v1, const Vector8 v2);
+static inline Vector8 vector8_ussub(const Vector8 v1, const Vector8 v2);
 #endif
 
 /*
@@ -99,6 +106,17 @@ 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 Vector8 vector8_pack_16(const Vector8 v1, const Vector8 v2);
+static inline Vector32 vector32_shift_left_nibble(const Vector32 v1);
+static inline Vector32 vector32_shift_right_nibble(const Vector32 v1);
+static inline Vector32 vector32_shift_right_byte(const Vector32 v1);
 #endif
 
 /*
@@ -128,6 +146,21 @@ 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.
  */
@@ -257,13 +290,32 @@ vector8_has_le(const Vector8 v, const uint8 c)
 	 * NUL bytes.  This approach is a workaround for the lack of unsigned
 	 * comparison instructions on some architectures.
 	 */
-	result = vector8_has_zero(vector8_ssub(v, vector8_broadcast(c)));
+	result = vector8_has_zero(vector8_ussub(v, vector8_broadcast(c)));
 #endif
 
 	Assert(assert_result == result);
 	return result;
 }
 
+/*
+ * Returns true if any elements in the vector are greater than or equal to the
+ * given scalar.
+ */
+#ifndef USE_NO_SIMD
+static inline bool
+vector8_has_ge(const Vector8 v, const uint8 c)
+{
+#ifdef USE_SSE2
+	Vector8		umax = _mm_max_epu8(v, vector8_broadcast(c));
+	Vector8		cmpe = _mm_cmpeq_epi8(umax, v);
+
+	return vector8_is_highbit_set(cmpe);
+#elif defined(USE_NEON)
+	return vmaxvq_u8(v) >= c;
+#endif
+}
+#endif							/* ! USE_NO_SIMD */
+
 /*
  * Return true if the high bit of any element is set
  */
@@ -358,15 +410,65 @@ 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
- * than zero, zero is returned instead).  For more information on saturation
- * arithmetic, see https://en.wikipedia.org/wiki/Saturation_arithmetic
+ * vectors using signed saturation (i.e., if the operation would yield a value
+ * less than -128, -128 is returned instead).  For more information on
+ * saturation arithmetic, see
+ * https://en.wikipedia.org/wiki/Saturation_arithmetic
  */
 #ifndef USE_NO_SIMD
 static inline Vector8
-vector8_ssub(const Vector8 v1, const Vector8 v2)
+vector8_sssub(const Vector8 v1, const Vector8 v2)
+{
+#ifdef USE_SSE2
+	return _mm_subs_epi8(v1, v2);
+#elif defined(USE_NEON)
+	return vqsubq_s8((int8x16_t) v1, (int8x16_t) v2);
+#endif
+}
+#endif							/* ! USE_NO_SIMD */
+
+/*
+ * Return the result of subtracting the respective elements of the input
+ * vectors using unsigned saturation (i.e., if the operation would yield a
+ * value less than zero, zero is returned instead).  For more information on
+ * saturation arithmetic, see
+ * https://en.wikipedia.org/wiki/Saturation_arithmetic
+ */
+#ifndef USE_NO_SIMD
+static inline Vector8
+vector8_ussub(const Vector8 v1, const Vector8 v2)
 {
 #ifdef USE_SSE2
 	return _mm_subs_epu8(v1, v2);
@@ -404,6 +506,23 @@ 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 +538,100 @@ 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 */
+
+/*
+ * Pack 16-bit elements in the given vectors into a single vector of 8-bit
+ * elements.  NB: The upper 8-bits of each 16-bit element must be zeros, else
+ * this will produce different results on different architectures.
+ */
+#ifndef USE_NO_SIMD
+static inline Vector8
+vector8_pack_16(const Vector8 v1, const Vector8 v2)
+{
+	Vector32	mask PG_USED_FOR_ASSERTS_ONLY = vector32_broadcast(0xff00ff00);
+
+	Assert(!vector8_has_ge(vector8_and(v1, mask), 1));
+	Assert(!vector8_has_ge(vector8_and(v2, mask), 1));
+#ifdef USE_SSE2
+	return _mm_packus_epi16(v1, v2);
+#elif defined(USE_NEON)
+	return vuzp1q_u8(v1, v2);
+#endif
+}
+#endif							/* ! USE_NO_SIMD */
+
+/*
+ * Unsigned shift left of each element in the vector by 4 bits.
+ */
+#ifndef USE_NO_SIMD
+static inline Vector32
+vector32_shift_left_nibble(const Vector32 v1)
+{
+#ifdef USE_SSE2
+	return _mm_slli_epi32(v1, 4);
+#elif defined(USE_NEON)
+	return vshlq_n_u32(v1, 4);
+#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 */
+
+/*
+ * Unsigned shift right of each element in the vector by 1 byte.
+ */
+#ifndef USE_NO_SIMD
+static inline Vector32
+vector32_shift_right_byte(const Vector32 v1)
+{
+#ifdef USE_SSE2
+	return _mm_srli_epi32(v1, 8);
+#elif defined(USE_NEON)
+	return vshrq_n_u32(v1, 8);
+#endif
+}
+#endif							/* ! USE_NO_SIMD */
+
 #endif							/* SIMD_H */
-- 
2.39.5 (Apple Git-154)


--1egPQYR2VaA9f9J/--