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>
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 @@
/* 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';