From ac827a2baa5e0c486b554cdee56c72624b499a40 Mon Sep 17 00:00:00 2001 From: Fredrik Holmqvist Date: Sun, 19 Aug 2012 11:30:23 +0200 Subject: [PATCH] Make strcmp do four byte comparisons on aligned strings. Used libMicro's strcmp test to evaluate performance: OPTS="-E -C 200 -S -W" bin/strcmp $OPTS -N "strcmp_10" -s 10 -I 10 bin/strcmp $OPTS -N "strcmp_100" -s 100 -I 20 bin/strcmp $OPTS -N "strcmp_1k" -s 1k -I 50 bin/strcmp $OPTS -N "strcmp_10k" -s 10k -I 800 bin/strcmp $OPTS -N "strcmp_1m" -s 1m -I 500000 bin/strcmp $OPTS -N "strcmp_10m" -s 10m -I 5000000 Before: prc thr usecs/call samples errors cnt/samp size strcmp_10 1 1 0.02510 201 0 10000 10 strcmp_100 1 1 0.17520 169 0 5000 100 strcmp_1k 1 1 1.67700 177 0 2000 1024 strcmp_10k 1 1 17.24800 194 0 125 10240 strcmp_1m 1 1 17892.00000 160 0 1 1048576 strcmp_10m 1 1 183136.00000 201 0 1 10485760 After: strcmp_10 1 1 0.01800 194 0 10000 10 strcmp_100 1 1 0.13540 190 0 5000 100 strcmp_1k 1 1 1.24950 188 0 2000 1024 strcmp_10k 1 1 12.85600 190 0 125 10240 strcmp_1m 1 1 12930.00000 170 0 1 1048576 strcmp_10m 1 1 134382.00000 195 0 1 10485760 --- src/system/libroot/posix/string/strcmp.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/src/system/libroot/posix/string/strcmp.c b/src/system/libroot/posix/string/strcmp.c index 63551164dc..cdba1d4f01 100644 --- a/src/system/libroot/posix/string/strcmp.c +++ b/src/system/libroot/posix/string/strcmp.c @@ -6,11 +6,28 @@ #include #include +#include +#define LACKS_ZERO_BYTE(value) \ + (((value - 0x01010101) & ~value & 0x80808080) == 0) + int strcmp(char const *a, char const *b) { + /* Make sure we don't pass page boundries on a or b when doing four byte + comparisons */ + if ((((addr_t)a) & 3) == 0 && (((addr_t)b) && 3) == 0) { + uint32* a32 = (uint32*)a; + uint32* b32 = (uint32*)b; + + while (LACKS_ZERO_BYTE(*a32)) { + int32 cmp = *a32++ - *b32++; + if (cmp != 0) + return cmp; + } + return *a32 - *b32; + } while (true) { int cmp = (unsigned char)*a - (unsigned char)*b++; if (cmp != 0 || *a++ == '\0')