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;