Replacement for snprintf

Rumbu rumbu at
Wed Oct 30 18:16:56 UTC 2019

On Wednesday, 30 October 2019 at 13:44:52 UTC, berni44 wrote:
> In PR 7222 [1] Robert Schadek suggested replacing the call to 
> snprinf in std.format with an own method written in D. During 
> the last days I took a deeper look into this and meanwhile I've 
> got a function that works for floats (and probably also 
> doubles, but I havn't tested that yet and it should also work 
> with reals if ucent would be available; without ucent I need a 
> workaround for real or fall back to BigInt).
> [...]

According to ieee754-2008:

"5.12.2 External decimal character sequences representing finite 


For binary formats, all conversions of H significant digits or 
fewer round correctly according to the applicable rounding 

Where H is 9 for single, 17 for double. IEE754 doesn't specify a 
H for reals.

That means that snprintf must use the current rounding mode that 
can be read using FloatingPointControl.rounding from std.math.

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