© 2011,2014 John Abbott
GNU Free Documentation License, Version 1.2

CoCoALib Documentation Index


User documentation

These functions are to help visualize integer and rational numbers in a more comprehensible format (as a decimal string). The SigFig argument is optional; its default value is 5.

Note: for values with large numerator or denominator it is quicker to convert the value to a RingElem belonging to a RingTwinFloat and then print the result. This approach offers less control over the output, and no guarantee of correct rounding.

Maintainer documentation

The function ScientificStr gives the clearest guarantees about the format used, but also produces the least humanly readable result. It uses MantissaAndExponent10 to do the conversion.

The function FloatStr is supposed to be the best general choice. It passes its args to ScientificStr in two situations: if the number is so large that padding would be needed before the decimal point; if the number is so small that the ScientificStr format would be shorter (i.e. if the exponent is less than -8).

The function DecimalStr is Anna's preferred choice. It uses ToString to convert to decimal.

Bugs, shortcomings and other ideas

These functions cannot be applied directly to a machine integer; to call them you have to convert explicitly into a BigInt (or BigRat).

The switch-over in FloatStr to scientific notation for "large" numbers is not ideal; in C the "g" format chooses the shorter between float and scientific formats. Is it worth the doing the same here?

Anna says an older version of DecimalStr would suppress trailing zeroes if the result is exact (e.g. DecimalStr(5/4,9) would produce 1.25 rather than 1.250000000. Is this a good idea?

These fns are too slow if N is a very large integer (or if numerator and/or denominator are very large). Converting to an mpf_t and printing that would be much faster (except in delicate rounding cases).

Main changes