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lib: vsprintf: optimize put_dec_trunc8() 

If you're going to have a conditional branch after each 32x32->64-bit
multiply, might as well shrink the code and make it a loop.

This also avoids using the long multiply for small integers.

(This leaves the comments in a confusing state, but that's a separate
patch to make review easier.)

Signed-off-by: George Spelvin <linux@horizon.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Rabin Vincent <rabin@rab.in>
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 17:12:30 -07:00 committed by Linus Torvalds
parent 2359172a75
commit cb239d0a97
1 changed files with 6 additions and 16 deletions
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22
lib/vsprintf.c
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@ -174,22 +174,12 @@ char *put_dec_trunc8(char *buf, unsigned r)
unsigned q;
/* Copy of previous function's body with added early returns */
q = (r * (uint64_t)0x1999999a) >> 32;
*buf++ = (r - 10 * q) + '0'; /* 2 */
if (q == 0)
return buf;
r = (q * (uint64_t)0x1999999a) >> 32;
*buf++ = (q - 10 * r) + '0'; /* 3 */
if (r == 0)
return buf;
q = (r * (uint64_t)0x1999999a) >> 32;
*buf++ = (r - 10 * q) + '0'; /* 4 */
if (q == 0)
return buf;
r = (q * (uint64_t)0x1999999a) >> 32;
*buf++ = (q - 10 * r) + '0'; /* 5 */
if (r == 0)
return buf;
while (r >= 10000) {
q = r + '0';
r = (r * (uint64_t)0x1999999a) >> 32;
*buf++ = q - 10*r;
}
q = (r * 0x199a) >> 16;
*buf++ = (r - 10 * q) + '0'; /* 6 */
if (q == 0)