• filipe oliveira's avatar
    optimizing d2string() and addReplyDouble() with grisu2: double to string... · 29380ff7
    filipe oliveira authored
    optimizing d2string() and addReplyDouble() with grisu2: double to string conversion based on Florian Loitsch's Grisu-algorithm (#10587)
    
    All commands / use cases that heavily rely on double to a string representation conversion,
    (e.g. meaning take a double-precision floating-point number like 1.5 and return a string like "1.5" ),
    could benefit from a performance boost by swapping snprintf(buf,len,"%.17g",value) by the
    equivalent [fpconv_dtoa](https://github.com/night-shift/fpconv) or any other algorithm that ensures
    100% coverage of conversion.
    
    This is a well-studied topic and Projects like MongoDB. RedPanda, PyTorch leverage libraries
    ( fmtlib ) that use the optimized double to string conversion underneath.
    
    
    The positive impact can be substantial. This PR uses the grisu2 approach ( grisu explained on
    https://www.cs.tufts.edu/~nr/cs257/archive/florian-loitsch/printf.pdf section 5 ). 
    
    test suite changes:
    Despite being compatible, in some cases it produces a different result from printf, and some tests
    had to be adjusted.
    one case is that `%.17g` (which means %e or %f which ever is shorter), chose to use `5000000000`
    instead of 5e+9, which sounds like a bug?
    In other cases, we changed TCL to compare numbers instead of strings to ignore minor rounding
    issues (`expr 0.8 == 0.79999999999999999`) 
    29380ff7
util.c 35.2 KB