float printing

float printing

[Christophe Raffalli]

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I have a small problem to read and write float in a file. I use the
format library and there is no way to write/read a float in hexadecimal
to be sure you read exactly the same float back from the file (a n bits
mantisse float may need n decimals to have an exact representation.
Just compute 1/2^n and count decimals).

The only way is to convert the float to string via Printf and then print
the string with Format.print_string.

Don't you think Pervasives and format should have a write/print_hexfloat
and Pervasives should have an input_hexfloat function ?

--
Christophe Raffalli
Université de Savoie
Batiment Le Chablais, bureau 21
73376 Le Bourget-du-Lac Cedex

tél: (33) 4 79 75 81 03
fax: (33) 4 79 75 87 42
mail: Christophe.Raffalli@univ-savoie.fr
www: http://www.lama.univ-savoie.fr/~RAFFALLI
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Re: [Caml-list] float printing

[Ken Rose]

Christophe Raffalli wrote:
> 
> I have a small problem to read and write float in a file. I use the
> format library and there is no way to write/read a float in hexadecimal
> to be sure you read exactly the same float back from the file (a n bits
> mantisse float may need n decimals to have an exact representation.
> Just compute 1/2^n and count decimals).
> 
> The only way is to convert the float to string via Printf and then print
> the string with Format.print_string.
> 
> Don't you think Pervasives and format should have a write/print_hexfloat
> and Pervasives should have an input_hexfloat function ?

Maybe Int64.bits_of_float and Int64.float_of_bits will do what you need.

  - ken

Re: [Caml-list] float printing

[Robert Roessler]

Christophe Raffalli wrote:

> I have a small problem to read and write float in a file. I use the
> format library and there is no way to write/read a float in hexadecimal
> to be sure you read exactly the same float back from the file (a n bits
> mantisse float may need n decimals to have an exact representation.
> Just compute 1/2^n and count decimals).
> 
> The only way is to convert the float to string via Printf and then print
> the string with Format.print_string.
> 
> Don't you think Pervasives and format should have a write/print_hexfloat
> and Pervasives should have an input_hexfloat function ?

How about the Int64 module?

val bits_of_float : float -> int64

This gives the exact "bits" for the IEEE double-precision float.

val float_of_bits : int64 -> float

This "reconstitutes" the float from the supplied 64-bit "integer".

There are also Int32-based versions of these, but with obviously lower 
precision - and the rounding method used to obtain Int32.bits_of_float 
is not specified.

Robert Roessler
roessler@rftp.com
http://www.rftp.com