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digitalmars.D - "%e" floating point format and exponent digits

reply "David Nadlinger" <see klickverbot.at> writes:
In Phobos, there are quite a few unit tests (std.format, 
std.json, ...) which assume that the %e floating point format 
zero-pads the exponent to (at least) two digits.

However, the printf-family functions in the MSVC and MinGW 
runtimes pad the exponent to *three* digits. For example, 
1.223e+24 is printed as "1.223e+024".

By extension, this also applies to the std.format (and thus 
std.stdio) floating point code, which relies on snprintf.

What is the correct fix here? Adjusting those unit tests? Doing 
something crazy along the lines of "if (result[$-4] == 'e' && 
result[$-3] == '0') { /+ trim zero +/ }"? (How) Is this handled 
on DMD/Win64?

The best way would probably be to just implement floating point 
printing in D as well, to isolate our code from such C runtime 
implementation differences.

David
Feb 20 2013
next sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 2/20/13, David Nadlinger <see klickverbot.at> wrote:
 In Phobos, there are quite a few unit tests (std.format,
 std.json, ...) which assume that the %e floating point format
 zero-pads the exponent to (at least) two digits.

I don't know about the exponent problem, but w.r.t. floating point there was a recent bug fixed where this source file: auto x = 1.0; Would be converted to this header file: auto x = 1; These are then different types. So I've changed how floating-point is written in DMD to always emit "1.0" rather than "1". This also improved diagnostics. But I wanted to always print at most two digits in this case (e.g. 1.00, 2.00, etc) but couldn't find a good way to do it with sprintf, so currently for floating-point e.g. "1" it prints "1.00000" in diagnostics and header files, which is excessive. Anyway I would definitely like to see floating-point printing synchronized across multiple compilers and also the D library, to be consistent everywhere.
Feb 20 2013
prev sibling parent "Don" <don nospam.com> writes:
On Wednesday, 20 February 2013 at 22:34:15 UTC, Andrej Mitrovic 
wrote:
 On 2/20/13, David Nadlinger <see klickverbot.at> wrote:
 In Phobos, there are quite a few unit tests (std.format,
 std.json, ...) which assume that the %e floating point format
 zero-pads the exponent to (at least) two digits.

I don't know about the exponent problem, but w.r.t. floating point there was a recent bug fixed where this source file: auto x = 1.0; Would be converted to this header file: auto x = 1; These are then different types. So I've changed how floating-point is written in DMD to always emit "1.0" rather than "1". This also improved diagnostics.% But I wanted to always print at most two digits in this case (e.g. 1.00, 2.00, etc) but couldn't find a good way to do it with sprintf, so currently for floating-point e.g. "1" it prints "1.00000" in diagnostics and header files, which is excessive. Anyway I would definitely like to see floating-point printing synchronized across multiple compilers and also the D library, to be consistent everywhere.

Another related issue is the format of %a. On Windows it prints 0x1.444p+99 but on Linux the same number is 0x0.A22p+99 That's much easier to deal with, because it's trivial to print the %A format. Correctly-rounded %e, %f is much more difficult, unfortunately (you need some simple bigint arithmetic).
Feb 22 2013