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-rw-r--r--lib/vsprintf.c173
1 files changed, 146 insertions, 27 deletions
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 017290241261..6b6734df6d2d 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -135,6 +135,103 @@ static int skip_atoi(const char **s)
return i;
}
+/* Decimal conversion is by far the most typical, and is used
+ * for /proc and /sys data. This directly impacts e.g. top performance
+ * with many processes running. We optimize it for speed
+ * using code from
+ * http://www.cs.uiowa.edu/~jones/bcd/decimal.html
+ * (with permission from the author, Douglas W. Jones). */
+
+/* Formats correctly any integer in [0,99999].
+ * Outputs from one to five digits depending on input.
+ * On i386 gcc 4.1.2 -O2: ~250 bytes of code. */
+static char* put_dec_trunc(char *buf, unsigned q)
+{
+ unsigned d3, d2, d1, d0;
+ d1 = (q>>4) & 0xf;
+ d2 = (q>>8) & 0xf;
+ d3 = (q>>12);
+
+ d0 = 6*(d3 + d2 + d1) + (q & 0xf);
+ q = (d0 * 0xcd) >> 11;
+ d0 = d0 - 10*q;
+ *buf++ = d0 + '0'; /* least significant digit */
+ d1 = q + 9*d3 + 5*d2 + d1;
+ if (d1 != 0) {
+ q = (d1 * 0xcd) >> 11;
+ d1 = d1 - 10*q;
+ *buf++ = d1 + '0'; /* next digit */
+
+ d2 = q + 2*d2;
+ if ((d2 != 0) || (d3 != 0)) {
+ q = (d2 * 0xd) >> 7;
+ d2 = d2 - 10*q;
+ *buf++ = d2 + '0'; /* next digit */
+
+ d3 = q + 4*d3;
+ if (d3 != 0) {
+ q = (d3 * 0xcd) >> 11;
+ d3 = d3 - 10*q;
+ *buf++ = d3 + '0'; /* next digit */
+ if (q != 0)
+ *buf++ = q + '0'; /* most sign. digit */
+ }
+ }
+ }
+ return buf;
+}
+/* Same with if's removed. Always emits five digits */
+static char* put_dec_full(char *buf, unsigned q)
+{
+ /* BTW, if q is in [0,9999], 8-bit ints will be enough, */
+ /* but anyway, gcc produces better code with full-sized ints */
+ unsigned d3, d2, d1, d0;
+ d1 = (q>>4) & 0xf;
+ d2 = (q>>8) & 0xf;
+ d3 = (q>>12);
+
+ /* Possible ways to approx. divide by 10 */
+ /* gcc -O2 replaces multiply with shifts and adds */
+ // (x * 0xcd) >> 11: 11001101 - shorter code than * 0x67 (on i386)
+ // (x * 0x67) >> 10: 1100111
+ // (x * 0x34) >> 9: 110100 - same
+ // (x * 0x1a) >> 8: 11010 - same
+ // (x * 0x0d) >> 7: 1101 - same, shortest code (on i386)
+
+ d0 = 6*(d3 + d2 + d1) + (q & 0xf);
+ q = (d0 * 0xcd) >> 11;
+ d0 = d0 - 10*q;
+ *buf++ = d0 + '0';
+ d1 = q + 9*d3 + 5*d2 + d1;
+ q = (d1 * 0xcd) >> 11;
+ d1 = d1 - 10*q;
+ *buf++ = d1 + '0';
+
+ d2 = q + 2*d2;
+ q = (d2 * 0xd) >> 7;
+ d2 = d2 - 10*q;
+ *buf++ = d2 + '0';
+
+ d3 = q + 4*d3;
+ q = (d3 * 0xcd) >> 11; /* - shorter code */
+ /* q = (d3 * 0x67) >> 10; - would also work */
+ d3 = d3 - 10*q;
+ *buf++ = d3 + '0';
+ *buf++ = q + '0';
+ return buf;
+}
+/* No inlining helps gcc to use registers better */
+static noinline char* put_dec(char *buf, unsigned long long num)
+{
+ while (1) {
+ unsigned rem;
+ if (num < 100000)
+ return put_dec_trunc(buf, num);
+ rem = do_div(num, 100000);
+ buf = put_dec_full(buf, rem);
+ }
+}
+
#define ZEROPAD 1 /* pad with zero */
#define SIGN 2 /* unsigned/signed long */
#define PLUS 4 /* show plus */
@@ -143,12 +240,14 @@ static int skip_atoi(const char **s)
#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 +255,6 @@ static char * number(char * buf, char * end, unsigned long long num, int base, i
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 +269,85 @@ static char * number(char * buf, char * end, unsigned long long num, int base, i
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++] = '0';
+ /* Generic code, for any base:
+ else do {
tmp[i++] = digits[do_div(num,base)];
+ } while (num != 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 { /* base 10 */
+ i = put_dec(tmp, num) - tmp;
+ }
+
+ /* 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) {
- if (buf < end)
- *buf = '0';
- ++buf;
- } else if (base==16) {
- if (buf < end)
- *buf = '0';
- ++buf;
+ /* "0x" / "0" prefix */
+ if (need_pfx) {
+ if (buf < end)
+ *buf = '0';
+ ++buf;
+ if (base == 16) {
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 +395,7 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
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;
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-18 16:46:37 +0100