mirror of https://gitee.com/openkylin/linux.git
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>
This commit is contained in:
Denis Vlasenko
Linus Torvalds
parent
4b4e5a1411
commit
b39a734097
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@ -143,12 +143,14 @@ static int skip_atoi(const char **s)
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#define SPECIAL 32 /* 0x */
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#define LARGE 64 /* use 'ABCDEF' instead of 'abcdef' */
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static char * number(char * buf, char * end, unsigned long long num, int base, int size, int precision, int type)
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static char *number(char *buf, char *end, unsigned long long num, int base, int size, int precision, int type)
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{
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char c,sign,tmp[66];
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char sign,tmp[66];
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const char *digits;
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static const char small_digits[] = "0123456789abcdefghijklmnopqrstuvwxyz";
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static const char large_digits[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
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/* we are called with base 8, 10 or 16, only, thus don't need "g..." */
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static const char small_digits[] = "0123456789abcdefx"; /* "ghijklmnopqrstuvwxyz"; */
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static const char large_digits[] = "0123456789ABCDEFX"; /* "GHIJKLMNOPQRSTUVWXYZ"; */
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int need_pfx = ((type & SPECIAL) && base != 10);
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int i;
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digits = (type & LARGE) ? large_digits : small_digits;
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@ -156,7 +158,6 @@ static char * number(char * buf, char * end, unsigned long long num, int base, i
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type &= ~ZEROPAD;
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if (base < 2 || base > 36)
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return NULL;
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c = (type & ZEROPAD) ? '0' : ' ';
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sign = 0;
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if (type & SIGN) {
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if ((signed long long) num < 0) {
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@ -171,64 +172,80 @@ static char * number(char * buf, char * end, unsigned long long num, int base, i
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size--;
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}
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}
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if (type & SPECIAL) {
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if (need_pfx) {
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size--;
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if (base == 16)
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size -= 2;
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else if (base == 8)
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size--;
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}
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/* generate full string in tmp[], in reverse order */
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i = 0;
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if (num == 0)
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tmp[i++]='0';
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else while (num != 0)
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tmp[i++] = digits[do_div(num,base)];
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tmp[i++] = '0';
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else if (base != 10) { /* 8 or 16 */
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int mask = base - 1;
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int shift = 3;
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if (base == 16) shift = 4;
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do {
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tmp[i++] = digits[((unsigned char)num) & mask];
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num >>= shift;
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} while (num);
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} else do { /* generic code, works for any base */
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tmp[i++] = digits[do_div(num,10 /*base*/)];
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} while (num);
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/* printing 100 using %2d gives "100", not "00" */
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if (i > precision)
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precision = i;
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/* leading space padding */
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size -= precision;
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if (!(type&(ZEROPAD+LEFT))) {
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while(size-->0) {
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if (!(type & (ZEROPAD+LEFT))) {
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while(--size >= 0) {
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if (buf < end)
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*buf = ' ';
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++buf;
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}
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}
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/* sign */
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if (sign) {
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if (buf < end)
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*buf = sign;
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++buf;
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}
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if (type & SPECIAL) {
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if (base==8) {
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/* "0x" / "0" prefix */
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if (need_pfx) {
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if (buf < end)
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*buf = '0';
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++buf;
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} else if (base==16) {
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if (base == 16) {
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if (buf < end)
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*buf = '0';
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++buf;
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if (buf < end)
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*buf = digits[33];
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*buf = digits[16]; /* for arbitrary base: digits[33]; */
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++buf;
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}
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}
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/* zero or space padding */
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if (!(type & LEFT)) {
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while (size-- > 0) {
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char c = (type & ZEROPAD) ? '0' : ' ';
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while (--size >= 0) {
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if (buf < end)
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*buf = c;
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++buf;
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}
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}
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while (i < precision--) {
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/* hmm even more zero padding? */
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while (i <= --precision) {
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if (buf < end)
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*buf = '0';
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++buf;
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}
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while (i-- > 0) {
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/* actual digits of result */
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while (--i >= 0) {
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if (buf < end)
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*buf = tmp[i];
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++buf;
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}
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while (size-- > 0) {
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/* trailing space padding */
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while (--size >= 0) {
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if (buf < end)
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*buf = ' ';
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++buf;
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@ -276,7 +293,7 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
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used for unknown buffer sizes. */
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if (unlikely((int) size < 0)) {
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/* There can be only one.. */
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static int warn = 1;
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static char warn = 1;
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WARN_ON(warn);
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warn = 0;
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return 0;
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