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 <[email protected]> Cc: Denys Vlasenko <[email protected]> Cc: Michal Nazarewicz <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
mrcsosa · Oct 5, 2012 · e49317d · e49317d
1 parent 6c0c0d4
commit e49317d
Showing 1 changed file with 3 additions and 2 deletions.
diff --git 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';