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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 <linux@horizon.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
George Spelvin 2012-10-04 17:12:27 -07:00 committed by Linus Torvalds
parent 6c0c0d4d10
commit e49317d415
1 changed files with 3 additions and 2 deletions
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5
lib/vsprintf.c
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@ -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';