diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/vsprintf.c | 246 |
1 files changed, 128 insertions, 118 deletions
diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 3a1e0843f9a2..c93ec8a035b3 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -33,6 +33,7 @@ #include <asm/page.h> /* for PAGE_SIZE */ #include <asm/sections.h> /* for dereference_function_descriptor() */ +#include <asm/byteorder.h> /* cpu_to_le16 */ #include <linux/string_helpers.h> #include "kstrtox.h" @@ -122,142 +123,147 @@ 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 ideas described at <http://www.cs.uiowa.edu/~jones/bcd/divide.html> - * (with permission from the author, Douglas W. Jones). +/* + * 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 by emitting + * two characters at a time, using a 200 byte lookup table. This + * roughly halves the number of multiplications compared to computing + * the digits one at a time. Implementation strongly inspired by the + * previous version, which in turn used ideas described at + * <http://www.cs.uiowa.edu/~jones/bcd/divide.html> (with permission + * from the author, Douglas W. Jones). + * + * It turns out there is precisely one 26 bit fixed-point + * approximation a of 64/100 for which x/100 == (x * (u64)a) >> 32 + * holds for all x in [0, 10^8-1], namely a = 0x28f5c29. The actual + * range happens to be somewhat larger (x <= 1073741898), but that's + * irrelevant for our purpose. + * + * For dividing a number in the range [10^4, 10^6-1] by 100, we still + * need a 32x32->64 bit multiply, so we simply use the same constant. + * + * For dividing a number in the range [100, 10^4-1] by 100, there are + * several options. The simplest is (x * 0x147b) >> 19, which is valid + * for all x <= 43698. */ -#if BITS_PER_LONG != 32 || BITS_PER_LONG_LONG != 64 -/* Formats correctly any integer in [0, 999999999] */ +static const u16 decpair[100] = { +#define _(x) (__force u16) cpu_to_le16(((x % 10) | ((x / 10) << 8)) + 0x3030) + _( 0), _( 1), _( 2), _( 3), _( 4), _( 5), _( 6), _( 7), _( 8), _( 9), + _(10), _(11), _(12), _(13), _(14), _(15), _(16), _(17), _(18), _(19), + _(20), _(21), _(22), _(23), _(24), _(25), _(26), _(27), _(28), _(29), + _(30), _(31), _(32), _(33), _(34), _(35), _(36), _(37), _(38), _(39), + _(40), _(41), _(42), _(43), _(44), _(45), _(46), _(47), _(48), _(49), + _(50), _(51), _(52), _(53), _(54), _(55), _(56), _(57), _(58), _(59), + _(60), _(61), _(62), _(63), _(64), _(65), _(66), _(67), _(68), _(69), + _(70), _(71), _(72), _(73), _(74), _(75), _(76), _(77), _(78), _(79), + _(80), _(81), _(82), _(83), _(84), _(85), _(86), _(87), _(88), _(89), + _(90), _(91), _(92), _(93), _(94), _(95), _(96), _(97), _(98), _(99), +#undef _ +}; + +/* + * This will print a single '0' even if r == 0, since we would + * immediately jump to out_r where two 0s would be written and one of + * them then discarded. This is needed by ip4_string below. All other + * callers pass a non-zero value of r. +*/ static noinline_for_stack -char *put_dec_full9(char *buf, unsigned q) +char *put_dec_trunc8(char *buf, unsigned r) { - unsigned r; + unsigned q; - /* - * Possible ways to approx. divide by 10 - * (x * 0x1999999a) >> 32 x < 1073741829 (multiply must be 64-bit) - * (x * 0xcccd) >> 19 x < 81920 (x < 262149 when 64-bit mul) - * (x * 0x6667) >> 18 x < 43699 - * (x * 0x3334) >> 17 x < 16389 - * (x * 0x199a) >> 16 x < 16389 - * (x * 0x0ccd) >> 15 x < 16389 - * (x * 0x0667) >> 14 x < 2739 - * (x * 0x0334) >> 13 x < 1029 - * (x * 0x019a) >> 12 x < 1029 - * (x * 0x00cd) >> 11 x < 1029 shorter code than * 0x67 (on i386) - * (x * 0x0067) >> 10 x < 179 - * (x * 0x0034) >> 9 x < 69 same - * (x * 0x001a) >> 8 x < 69 same - * (x * 0x000d) >> 7 x < 69 same, shortest code (on i386) - * (x * 0x0007) >> 6 x < 19 - * See <http://www.cs.uiowa.edu/~jones/bcd/divide.html> - */ - r = (q * (uint64_t)0x1999999a) >> 32; - *buf++ = (q - 10 * r) + '0'; /* 1 */ - q = (r * (uint64_t)0x1999999a) >> 32; - *buf++ = (r - 10 * q) + '0'; /* 2 */ - r = (q * (uint64_t)0x1999999a) >> 32; - *buf++ = (q - 10 * r) + '0'; /* 3 */ - q = (r * (uint64_t)0x1999999a) >> 32; - *buf++ = (r - 10 * q) + '0'; /* 4 */ - r = (q * (uint64_t)0x1999999a) >> 32; - *buf++ = (q - 10 * r) + '0'; /* 5 */ - /* Now value is under 10000, can avoid 64-bit multiply */ - q = (r * 0x199a) >> 16; - *buf++ = (r - 10 * q) + '0'; /* 6 */ - r = (q * 0xcd) >> 11; - *buf++ = (q - 10 * r) + '0'; /* 7 */ - q = (r * 0xcd) >> 11; - *buf++ = (r - 10 * q) + '0'; /* 8 */ - *buf++ = q + '0'; /* 9 */ + /* 1 <= r < 10^8 */ + if (r < 100) + goto out_r; + + /* 100 <= r < 10^8 */ + q = (r * (u64)0x28f5c29) >> 32; + *((u16 *)buf) = decpair[r - 100*q]; + buf += 2; + + /* 1 <= q < 10^6 */ + if (q < 100) + goto out_q; + + /* 100 <= q < 10^6 */ + r = (q * (u64)0x28f5c29) >> 32; + *((u16 *)buf) = decpair[q - 100*r]; + buf += 2; + + /* 1 <= r < 10^4 */ + if (r < 100) + goto out_r; + + /* 100 <= r < 10^4 */ + q = (r * 0x147b) >> 19; + *((u16 *)buf) = decpair[r - 100*q]; + buf += 2; +out_q: + /* 1 <= q < 100 */ + r = q; +out_r: + /* 1 <= r < 100 */ + *((u16 *)buf) = decpair[r]; + buf += 2; + if (buf[-1] == '0') + buf--; return buf; } -#endif -/* Similar to above but do not pad with zeros. - * Code can be easily arranged to print 9 digits too, but our callers - * always call put_dec_full9() instead when the number has 9 decimal digits. - */ +#if BITS_PER_LONG == 64 && BITS_PER_LONG_LONG == 64 static noinline_for_stack -char *put_dec_trunc8(char *buf, unsigned r) +char *put_dec_full8(char *buf, unsigned r) { unsigned q; - /* Copy of previous function's body with added early returns */ - while (r >= 10000) { - q = r + '0'; - r = (r * (uint64_t)0x1999999a) >> 32; - *buf++ = q - 10*r; - } + /* 0 <= r < 10^8 */ + q = (r * (u64)0x28f5c29) >> 32; + *((u16 *)buf) = decpair[r - 100*q]; + buf += 2; - q = (r * 0x199a) >> 16; /* r <= 9999 */ - *buf++ = (r - 10 * q) + '0'; - if (q == 0) - return buf; - r = (q * 0xcd) >> 11; /* q <= 999 */ - *buf++ = (q - 10 * r) + '0'; - if (r == 0) - return buf; - q = (r * 0xcd) >> 11; /* r <= 99 */ - *buf++ = (r - 10 * q) + '0'; - if (q == 0) - return buf; - *buf++ = q + '0'; /* q <= 9 */ - return buf; -} + /* 0 <= q < 10^6 */ + r = (q * (u64)0x28f5c29) >> 32; + *((u16 *)buf) = decpair[q - 100*r]; + buf += 2; -/* There are two algorithms to print larger numbers. - * One is generic: divide by 1000000000 and repeatedly print - * groups of (up to) 9 digits. It's conceptually simple, - * but requires a (unsigned long long) / 1000000000 division. - * - * Second algorithm splits 64-bit unsigned long long into 16-bit chunks, - * manipulates them cleverly and generates groups of 4 decimal digits. - * It so happens that it does NOT require long long division. - * - * If long is > 32 bits, division of 64-bit values is relatively easy, - * and we will use the first algorithm. - * If long long is > 64 bits (strange architecture with VERY large long long), - * second algorithm can't be used, and we again use the first one. - * - * Else (if long is 32 bits and long long is 64 bits) we use second one. - */ + /* 0 <= r < 10^4 */ + q = (r * 0x147b) >> 19; + *((u16 *)buf) = decpair[r - 100*q]; + buf += 2; -#if BITS_PER_LONG != 32 || BITS_PER_LONG_LONG != 64 - -/* First algorithm: generic */ + /* 0 <= q < 100 */ + *((u16 *)buf) = decpair[q]; + buf += 2; + return buf; +} -static +static noinline_for_stack char *put_dec(char *buf, unsigned long long n) { - if (n >= 100*1000*1000) { - while (n >= 1000*1000*1000) - buf = put_dec_full9(buf, do_div(n, 1000*1000*1000)); - if (n >= 100*1000*1000) - return put_dec_full9(buf, n); - } + if (n >= 100*1000*1000) + buf = put_dec_full8(buf, do_div(n, 100*1000*1000)); + /* 1 <= n <= 1.6e11 */ + if (n >= 100*1000*1000) + buf = put_dec_full8(buf, do_div(n, 100*1000*1000)); + /* 1 <= n < 1e8 */ return put_dec_trunc8(buf, n); } -#else +#elif BITS_PER_LONG == 32 && BITS_PER_LONG_LONG == 64 -/* Second algorithm: valid only for 64-bit long longs */ - -/* See comment in put_dec_full9 for choice of constants */ -static noinline_for_stack -void put_dec_full4(char *buf, unsigned q) +static void +put_dec_full4(char *buf, unsigned r) { - unsigned r; - r = (q * 0xccd) >> 15; - buf[0] = (q - 10 * r) + '0'; - q = (r * 0xcd) >> 11; - buf[1] = (r - 10 * q) + '0'; - r = (q * 0xcd) >> 11; - buf[2] = (q - 10 * r) + '0'; - buf[3] = r + '0'; + unsigned q; + + /* 0 <= r < 10^4 */ + q = (r * 0x147b) >> 19; + *((u16 *)buf) = decpair[r - 100*q]; + buf += 2; + /* 0 <= q < 100 */ + *((u16 *)buf) = decpair[q]; } /* @@ -265,9 +271,9 @@ void put_dec_full4(char *buf, unsigned q) * The approximation x/10000 == (x * 0x346DC5D7) >> 43 * holds for all x < 1,128,869,999. The largest value this * helper will ever be asked to convert is 1,125,520,955. - * (d1 in the put_dec code, assuming n is all-ones). + * (second call in the put_dec code, assuming n is all-ones). */ -static +static noinline_for_stack unsigned put_dec_helper4(char *buf, unsigned x) { uint32_t q = (x * (uint64_t)0x346DC5D7) >> 43; @@ -294,6 +300,8 @@ char *put_dec(char *buf, unsigned long long n) d2 = (h ) & 0xffff; d3 = (h >> 16); /* implicit "& 0xffff" */ + /* n = 2^48 d3 + 2^32 d2 + 2^16 d1 + d0 + = 281_4749_7671_0656 d3 + 42_9496_7296 d2 + 6_5536 d1 + d0 */ q = 656 * d3 + 7296 * d2 + 5536 * d1 + ((uint32_t)n & 0xffff); q = put_dec_helper4(buf, q); @@ -323,7 +331,8 @@ char *put_dec(char *buf, unsigned long long n) */ int num_to_str(char *buf, int size, unsigned long long num) { - char tmp[sizeof(num) * 3]; + /* put_dec requires 2-byte alignment of the buffer. */ + char tmp[sizeof(num) * 3] __aligned(2); int idx, len; /* put_dec() may work incorrectly for num = 0 (generate "", not "0") */ @@ -384,7 +393,8 @@ static noinline_for_stack char *number(char *buf, char *end, unsigned long long num, struct printf_spec spec) { - char tmp[3 * sizeof(num)]; + /* put_dec requires 2-byte alignment of the buffer. */ + char tmp[3 * sizeof(num)] __aligned(2); char sign; char locase; int need_pfx = ((spec.flags & SPECIAL) && spec.base != 10); @@ -944,7 +954,7 @@ char *ip4_string(char *p, const u8 *addr, const char *fmt) break; } for (i = 0; i < 4; i++) { - char temp[3]; /* hold each IP quad in reverse order */ + char temp[4] __aligned(2); /* hold each IP quad in reverse order */ int digits = put_dec_trunc8(temp, addr[index]) - temp; if (leading_zeros) { if (digits < 3) |