From e49317d415f5a44bad8377a208d61902d752303e Mon Sep 17 00:00:00 2001 From: George Spelvin Date: Thu, 4 Oct 2012 17:12:27 -0700 Subject: [PATCH] lib: vsprintf: optimize division by 10 for small integers Shrink the reciprocal approximations used in put_dec_full4() based on the comments in put_dec_full9(). Signed-off-by: George Spelvin Cc: Denys Vlasenko Cc: Michal Nazarewicz Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/vsprintf.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 0e33754..67e74cb 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'; -- 2.7.4