On Tue, Jan 14, 2025 at 11:57 PM Nathan Bossart <nathandboss...@gmail.com> wrote: > > On Tue, Jan 14, 2025 at 12:59:04AM -0500, Tom Lane wrote: > > John Naylor <johncnaylo...@gmail.com> writes: > >> We can do about as well simply by changing the nibble lookup to a byte > >> lookup, which works on every compiler and architecture: > > Nice. I tried enabling auto-vectorization and loop unrolling on top of > this patch, and the numbers looked the same. I think we'd need CPU > intrinsics or an even bigger lookup table to do any better.
Thanks for looking further! Yeah, I like that the table is still only 512 bytes. > > I didn't attempt to verify your patch, but I do prefer addressing > > this issue in a machine-independent fashion. I also like the brevity > > of the patch (though it could do with some comments perhaps, not that > > the existing code has any). > > +1 Okay, I added a comment. I also agree with Michael that my quick one-off was a bit hard to read so I've cleaned it up a bit. I plan to commit the attached by Friday, along with any bikeshedding that happens by then. -- John Naylor Amazon Web Services
From a62aea5fdbfbd215435ddc4c294897caa292b6f7 Mon Sep 17 00:00:00 2001 From: John Naylor <john.nay...@postgresql.org> Date: Wed, 15 Jan 2025 13:28:26 +0700 Subject: [PATCH v3] Speed up hex_encode with bytewise lookup Previously, hex_encode looked up each nibble of the input separately. We now use a larger lookup table containing the two-byte encoding of every possible input byte, resulting in a 1/3 reduction in encoding time. Reviewed by Michael Paquier, Tom Lane, and Nathan Bossart Discussion: https://postgr.es/m/CANWCAZZvXuJMgqMN4u068Yqa19CEjS31tQKZp_qFFFbgYfaXqQ%40mail.gmail.com --- src/backend/utils/adt/encode.c | 29 ++++++++++++++++++++++++++--- 1 file changed, 26 insertions(+), 3 deletions(-) diff --git a/src/backend/utils/adt/encode.c b/src/backend/utils/adt/encode.c index 4a6fcb56cd..7fee154b0d 100644 --- a/src/backend/utils/adt/encode.c +++ b/src/backend/utils/adt/encode.c @@ -145,7 +145,23 @@ binary_decode(PG_FUNCTION_ARGS) * HEX */ -static const char hextbl[] = "0123456789abcdef"; +static const char hextbl[512] = +"000102030405060708090a0b0c0d0e0f" +"101112131415161718191a1b1c1d1e1f" +"202122232425262728292a2b2c2d2e2f" +"303132333435363738393a3b3c3d3e3f" +"404142434445464748494a4b4c4d4e4f" +"505152535455565758595a5b5c5d5e5f" +"606162636465666768696a6b6c6d6e6f" +"707172737475767778797a7b7c7d7e7f" +"808182838485868788898a8b8c8d8e8f" +"909192939495969798999a9b9c9d9e9f" +"a0a1a2a3a4a5a6a7a8a9aaabacadaeaf" +"b0b1b2b3b4b5b6b7b8b9babbbcbdbebf" +"c0c1c2c3c4c5c6c7c8c9cacbcccdcecf" +"d0d1d2d3d4d5d6d7d8d9dadbdcdddedf" +"e0e1e2e3e4e5e6e7e8e9eaebecedeeef" +"f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff"; static const int8 hexlookup[128] = { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, @@ -165,9 +181,16 @@ hex_encode(const char *src, size_t len, char *dst) while (src < end) { - *dst++ = hextbl[(*src >> 4) & 0xF]; - *dst++ = hextbl[*src & 0xF]; + unsigned char usrc = *((unsigned char *) src); + + /* + * Each input byte results in two output bytes, so we use the unsigned + * input byte multiplied by two as the lookup key. + */ + memcpy(dst, &hextbl[2 * usrc], 2); + src++; + dst += 2; } return (uint64) len * 2; } -- 2.47.1
