Performance regression on integer formatting

[vitaut]

fmt::format performance on integer formatting is down to sprintf level. Need to investigate and fix before 2.0.

['Method'                      , 'Time, s' , 'Time ratio' ],
['fmt::FormatInt'              ,   0.130368,           1.0],
['cppx::decimal_from'          ,   0.160879, 1.23403749386],
['karma::generate'             ,   0.163209, 1.25190997791],
['fmt::Writer'                 ,   0.201434, 1.54511843397],
['karma::generate+std::string' ,   0.319312, 2.44931271478],
['fmt::Writer+std::string'     ,   0.369383, 2.83338702749],
['ltoa'                        ,   0.487947, 3.74284333579],
['itostr'                      ,    0.62576,  4.7999509082],
['sprintf'                     ,   0.887256, 6.80578055965],
['boost::lexical_cast'         ,   0.952595, 7.30696950172],
['fmt::format'                 ,   0.995007,  7.6322947349],
['sprintf+std::string'         ,    1.04289, 7.99958578792],
['std::stringstream'           ,    1.25203, 9.60381381934],
['std::to_string'              ,    1.38192, 10.6001472754],
['boost::format'               ,    4.40774, 33.8099840452]

[vitaut]

There was a minor performance regression in 1b80148:

['Method'                      , 'Time, s' , 'Time ratio' ],
['fmt::FormatInt'              ,   0.141162,           1.0],
['karma::generate'             ,   0.162126,  1.1485102223],
['cppx::decimal_from'          ,   0.167754, 1.18837930888],
['fmt::Writer'                 ,   0.192687, 1.36500616313], <---
['karma::generate+std::string' ,   0.321725, 2.27911902637],
['fmt::Writer+std::string'     ,   0.387114, 2.74233858971],
['fmt::format'                 ,   0.462457,  3.2760728808],
['ltoa'                        ,   0.487219, 3.45148836089],
['itostr'                      ,   0.665112, 4.71169294853],
['sprintf'                     ,   0.894235, 6.33481390176],
['boost::lexical_cast'         ,    1.04254, 7.38541533841],
['sprintf+std::string'         ,    1.04865, 7.42869894164],
['std::stringstream'           ,    1.27094, 9.00341451665],
['std::to_string'              ,    1.34653, 9.53889857044],
['boost::format'               ,    4.40832, 31.2288009521]

[vitaut]

Improved in 922fe90:

['Method'                      , 'Time, s' , 'Time ratio' ],
['fmt::FormatInt'              ,   0.130876,           1.0],
['cppx::decimal_from'          ,   0.161449,  1.2336027996],
['karma::generate'             ,   0.161707, 1.23557413124],
['fmt::Writer'                 ,    0.17376, 1.32766893854], <---
['karma::generate+std::string' ,   0.319278, 2.43954582964],
['fmt::Writer+std::string'     ,   0.344104, 2.62923683487],
['ltoa'                        ,   0.487851, 3.72758183319],
['itostr'                      ,    0.61139, 4.67152113451],
['sprintf'                     ,   0.874873, 6.68474739448],
['boost::lexical_cast'         ,   0.924096, 7.06085149302],
['fmt::format'                 ,   0.992863, 7.58628778386],
['sprintf+std::string'         ,     1.0205,   7.797457135],
['std::stringstream'           ,    1.22714, 9.37635624561],
['std::to_string'              ,    1.31599, 10.0552431309],
['boost::format'               ,    4.20408, 32.1226198845]

[vitaut]

As of 58fcf0c, integer formatting in fmt::Writer is back to normal (aka super fast):

['Method'                      , 'Time, s' , 'Time ratio' ],
['fmt::FormatInt'              ,   0.130366,           1.0],
['fmt::Writer'                 ,    0.15293, 1.17308193854], <---
['cppx::decimal_from'          ,   0.158245, 1.21385177117],
['karma::generate'             ,   0.163913, 1.25732936502],
['karma::generate+std::string' ,   0.317622, 2.43638678797],
['fmt::Writer+std::string'     ,   0.327253, 2.51026341224],
['ltoa'                        ,   0.489808, 3.75717595078],
['itostr'                      ,   0.615213,  4.7191215501],
['sprintf'                     ,   0.883171, 6.77455011276],
['fmt::format'                 ,   0.956393, 7.33621496402],
['boost::lexical_cast'         ,   0.994558, 7.62896767562],
['sprintf+std::string'         ,    1.02793, 7.88495466609],
['std::to_string'              ,    1.34569, 10.3224000123],
['std::stringstream'           ,    1.38597, 10.6313762791],
['boost::format'               ,    4.07773, 31.2790911741]

[vitaut]

This is fixed, but need to look into fmt::format: #193