diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/vsprintf.c | 108 |
1 files changed, 105 insertions, 3 deletions
diff --git a/lib/vsprintf.c b/lib/vsprintf.c index e94b4bd25bc..6b6734df6d2 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 */ @@ -182,6 +279,11 @@ static char *number(char *buf, char *end, unsigned long long num, int base, int i = 0; if (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; @@ -190,9 +292,9 @@ static char *number(char *buf, char *end, unsigned long long num, int base, int 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); + } else { /* base 10 */ + i = put_dec(tmp, num) - tmp; + } /* printing 100 using %2d gives "100", not "00" */ if (i > precision) |