added fast_istr for fast int_to_string

This commit is contained in:
gabi 2014-10-14 03:43:50 +03:00
parent 8139d01142
commit 793d16d547
1 changed files with 103 additions and 0 deletions

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@ -0,0 +1,103 @@
#pragma once
#include <string>
//Fast to int to string
//Source: http://stackoverflow.com/a/4351484/192001
//Modified version to pad zeros according to min_size
namespace c11log {
namespace details {
const char digit_pairs[201] = {
"00010203040506070809"
"10111213141516171819"
"20212223242526272829"
"30313233343536373839"
"40414243444546474849"
"50515253545556575859"
"60616263646566676869"
"70717273747576777879"
"80818283848586878889"
"90919293949596979899"
};
inline std::string& fast_itostr(int n, std::string& s, int padding)
{
if (n == 0)
{
s = "0";
return s;
}
int sign = -(n < 0);
unsigned int val = (n^sign) - sign;
int size;
if (val >= 10000)
{
if (val >= 10000000)
{
if (val >= 1000000000)
size = 10;
else if (val >= 100000000)
size = 9;
else
size = 8;
}
else
{
if (val >= 1000000)
size = 7;
else if (val >= 100000)
size = 6;
else
size = 5;
}
}
else
{
if (val >= 100)
{
if (val >= 1000)
size = 4;
else
size = 3;
}
else
{
if (val >= 10)
size = 2;
else
size = 1;
}
}
size -= sign;
if (size < padding)
size = padding;
s.resize(size);
char* c = &s[0];
if (sign)
*c = '-';
c += size - 1;
while (val >= 100)
{
int pos = val % 100;
val /= 100;
*(short*)(c - 1) = *(short*)(digit_pairs + 2 * pos);
c -= 2;
}
while (val > 0)
{
*c-- = '0' + (val % 10);
val /= 10;
}
while (c >= s.data())
*c-- = '0';
return s;
}
}
}