Messages in this thread Patch in this message | | | Date | Thu, 27 May 2010 12:07:29 +0200 | From | Fredrik Gustafsson <> | Subject | hex_to_bin speedup |
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Hi, I looked a bit at the newly added hex_to_bin function in lib/hexdump.c. I do believe this is a speedup (at least according to my benchmark[1]).
However in the comments to commit 903788892ea0fc7fcaf7e8e5fac9a77379fc215b you can read "[akpm@linux-foundation.org: use tolower(), saving 3 bytes, test the more common case first - it's quicker]"
I don't know the change that akpm has done, so I'm unsure if there's any problems that I miss with my patch.
-- iveqy
[1] Benchmark
#include <sys/time.h> #include <stdio.h>
int main() { struct timeval start, end; int i,itr; itr = 100000; char c = 'A'; time_t diff; gettimeofday(&start,NULL); for(i = 0; i < itr; i++) { if((c >= 'A') && (c <= 'F')) {} } gettimeofday(&end,NULL); diff = end.tv_usec - start.tv_usec; printf("if-statement: %d ms\n",diff); gettimeofday(&start,NULL); for(i = 0; i < itr; i++) { c = tolower(c); } gettimeofday(&end,NULL); diff = end.tv_usec - start.tv_usec; printf("tolower(): %d ms\n",diff); }
[2] Patch
This is faster (at least on i686). --- lib/hexdump.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/lib/hexdump.c b/lib/hexdump.c index 5d7a480..f01d11c 100644 --- a/lib/hexdump.c +++ b/lib/hexdump.c @@ -26,9 +26,10 @@ int hex_to_bin(char ch) { if ((ch >= '0') && (ch <= '9')) return ch - '0'; - ch = tolower(ch); if ((ch >= 'a') && (ch <= 'f')) return ch - 'a' + 10; + if ((ch >= 'A') && (ch <= 'F')) + return ch - 'A' + 10; return -1; } EXPORT_SYMBOL(hex_to_bin);
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