Messages in this thread Patch in this message | | | From | George Spelvin <> | Subject | [PATCH 1/4] lib: vsprintf: Optimize division by 10 for small integers. | Date | Fri, 3 Aug 2012 01:21:08 -0400 |
| |
Shrink the reciprocal approximations used in put_dec_full4 based on the comments in put_dec_full9.
Signed-off-by: George Spelvin <linux@horizon.com> Cc: Denys Vlasenko <vda.linux@googlemail.com> Cc: Michal Nazarewicz <mina86@mina86.com> --- lib/vsprintf.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
I was looking over the code and noticed that the constants could be smaller.
diff --git a/lib/vsprintf.c b/lib/vsprintf.c index c3f36d41..2f32fe8 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -243,13 +243,14 @@ char *put_dec(char *buf, unsigned long long n) /* Second algorithm: valid only for 64-bit long longs */ +/* See comment in put_dec_full9 for choice of constants */ static noinline_for_stack char *put_dec_full4(char *buf, unsigned q) { unsigned r; - r = (q * 0xcccd) >> 19; + r = (q * 0xccd) >> 15; *buf++ = (q - 10 * r) + '0'; - q = (r * 0x199a) >> 16; + q = (r * 0xcd) >> 11; *buf++ = (r - 10 * q) + '0'; r = (q * 0xcd) >> 11; *buf++ = (q - 10 * r) + '0'; -- 1.7.10.4
| |