vsprintf.c: optimizing, part 1 (easy and obvious stuff)
* There is no point in having full "0...9a...z" constant vector,
if we use only "0...9a...f" (and "x" for "0x").
* Post-decrement usually needs a few more instructions, so use
pre decrement instead where makes sense:
- while (i < precision--) {
+ while (i <= --precision) {
* if base != 10 (=> base 8 or 16), we can avoid using division
in a loop and use mask/shift, obtaining much faster conversion.
(More complex optimization for base 10 case is in the second patch).
Overall, size vsprintf.o shows ~80 bytes smaller text section
with this patch applied.
Signed-off-by: Douglas W Jones <jones@cs.uiowa.edu>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.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 0172902..e94b4bd 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -143,12 +143,14 @@
#define SPECIAL 32 /* 0x */
#define LARGE 64 /* use 'ABCDEF' instead of 'abcdef' */
-static char * number(char * buf, char * end, unsigned long long num, int base, int size, int precision, int type)
+static char *number(char *buf, char *end, unsigned long long num, int base, int size, int precision, int type)
{
- char c,sign,tmp[66];
+ char sign,tmp[66];
const char *digits;
- static const char small_digits[] = "0123456789abcdefghijklmnopqrstuvwxyz";
- static const char large_digits[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+ /* we are called with base 8, 10 or 16, only, thus don't need "g..." */
+ static const char small_digits[] = "0123456789abcdefx"; /* "ghijklmnopqrstuvwxyz"; */
+ static const char large_digits[] = "0123456789ABCDEFX"; /* "GHIJKLMNOPQRSTUVWXYZ"; */
+ int need_pfx = ((type & SPECIAL) && base != 10);
int i;
digits = (type & LARGE) ? large_digits : small_digits;
@@ -156,7 +158,6 @@
type &= ~ZEROPAD;
if (base < 2 || base > 36)
return NULL;
- c = (type & ZEROPAD) ? '0' : ' ';
sign = 0;
if (type & SIGN) {
if ((signed long long) num < 0) {
@@ -171,64 +172,80 @@
size--;
}
}
- if (type & SPECIAL) {
+ if (need_pfx) {
+ size--;
if (base == 16)
- size -= 2;
- else if (base == 8)
size--;
}
+
+ /* generate full string in tmp[], in reverse order */
i = 0;
if (num == 0)
- tmp[i++]='0';
- else while (num != 0)
- tmp[i++] = digits[do_div(num,base)];
+ tmp[i++] = '0';
+ else if (base != 10) { /* 8 or 16 */
+ int mask = base - 1;
+ int shift = 3;
+ if (base == 16) shift = 4;
+ do {
+ tmp[i++] = digits[((unsigned char)num) & mask];
+ num >>= shift;
+ } while (num);
+ } else do { /* generic code, works for any base */
+ tmp[i++] = digits[do_div(num,10 /*base*/)];
+ } while (num);
+
+ /* printing 100 using %2d gives "100", not "00" */
if (i > precision)
precision = i;
+ /* leading space padding */
size -= precision;
- if (!(type&(ZEROPAD+LEFT))) {
- while(size-->0) {
+ if (!(type & (ZEROPAD+LEFT))) {
+ while(--size >= 0) {
if (buf < end)
*buf = ' ';
++buf;
}
}
+ /* sign */
if (sign) {
if (buf < end)
*buf = sign;
++buf;
}
- if (type & SPECIAL) {
- if (base==8) {
+ /* "0x" / "0" prefix */
+ if (need_pfx) {
+ if (buf < end)
+ *buf = '0';
+ ++buf;
+ if (base == 16) {
if (buf < end)
- *buf = '0';
- ++buf;
- } else if (base==16) {
- if (buf < end)
- *buf = '0';
- ++buf;
- if (buf < end)
- *buf = digits[33];
+ *buf = digits[16]; /* for arbitrary base: digits[33]; */
++buf;
}
}
+ /* zero or space padding */
if (!(type & LEFT)) {
- while (size-- > 0) {
+ char c = (type & ZEROPAD) ? '0' : ' ';
+ while (--size >= 0) {
if (buf < end)
*buf = c;
++buf;
}
}
- while (i < precision--) {
+ /* hmm even more zero padding? */
+ while (i <= --precision) {
if (buf < end)
*buf = '0';
++buf;
}
- while (i-- > 0) {
+ /* actual digits of result */
+ while (--i >= 0) {
if (buf < end)
*buf = tmp[i];
++buf;
}
- while (size-- > 0) {
+ /* trailing space padding */
+ while (--size >= 0) {
if (buf < end)
*buf = ' ';
++buf;
@@ -276,7 +293,7 @@
used for unknown buffer sizes. */
if (unlikely((int) size < 0)) {
/* There can be only one.. */
- static int warn = 1;
+ static char warn = 1;
WARN_ON(warn);
warn = 0;
return 0;