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 0e337541f005d8f29a36434dae555b7477d12164..67e74cbefa9047dc9de24dac7c6ad71520c0d0d1 100644 (file)
--- 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';