fix: correct %g and %e exponent for powers of 10#1324
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Motivation: %g % 1000000 produced "1000000" instead of "1e+06", and %.2g % 1000 produced "10e+02" instead of "1e+03". Root cause: std.log(x)/std.log(10) suffers from floating-point imprecision for powers of 10 (e.g. log(1000000)/log(10) = 5.999999... instead of 6), causing std.floor to round down incorrectly. Modification: Added 1e-12 epsilon before std.floor in exponent calculation in both render_float_sci and the %g format handler. The epsilon is large enough to correct floating-point error (~1e-15) but small enough to not affect non-power-of-10 values. Result: - "%g" % 1000000 → "1e+06" (was "1000000") - "%.2g" % 1000 → "1e+03" (was "10e+02") - "%e" % 1000000 → "1.000000e+06" (was "1.000000e+05" with wrong mantissa) - All other %g/%e cases unchanged.
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Motivation
%g % 1000000produces"1000000"instead of"1e+06", and%.2g % 1000produces"10e+02"instead of"1e+03". Cprintfand Python both produce the correct output.Root cause:
std.log(x)/std.log(10)suffers from floating-point imprecision for powers of 10:log(1000000)/log(10)=5.9999999999999991(should be 6)log(1000)/log(10)=2.9999999999999996(should be 3)std.floorthen rounds these down incorrectly.Modification
Added
1e-12epsilon beforestd.floorin the exponent calculation, in two places:render_float_sci(used by%e/%E)%g/%Gformat handlerThe epsilon is ~1000x the floating-point error (~1e-15) but far too small to affect non-power-of-10 values.
Result
"%g" % 1000000"1000000""1e+06""1e+06""%.2g" % 1000"10e+02""1e+03""1e+03""%e" % 1000000"1.000000e+05"(wrong)"1.000000e+06""1.000000e+06""%G" % 1000000"10E+05""1E+06""1E+06"All other
%g/%ecases produce identical output before and after this fix.Test plan
printfand Python%gfor: 0, ±1000000, 1e10, 1e-10, 123456, 999999, 3.14, various precision specifiers%f,%d,%x,%o,%c,%sformat codes