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Source for wiki FloatPrecision version 4











== Multiple inexact-number precisions ==

Scheme (before R7RS) and Common Lisp require that implementations understand short-float, single-float, double-float and long-float syntax.  These are written by replacing the `e` of exponential notation with an `s`, `f`, `d`, or `l` respectively.  However, there is no requirement that any of these be distinct, only that they be consistent: short-floats cannot have more precision than long-floats, for example.  Common Lisp requires that `e` notation be equivalent to `f` notation by default; Scheme has no such requirement.

I asked the usual Schemes and some Common Lisps to evaluate `3.1415926535897932385s0`,  `3.1415926535897932385f0`, `3.1415926535897932385d0`, and `3.1415926535897932385l0`, where the numeric value is a 64-bit version of ''π''.  Common Lisps were asked about precision directly using the standard `float-bits` procedure.  For Scheme, I inferred how many bits of precision were provided by the answers.  Here are the results (note that IEEE doubles are 53-bit precision and IEEE singles are 24-bit precision):

All four numbers are the same and have 53-bit precision:  Gauche, Gambit, Chicken (with or without the numbers egg)*, Guile*, Kawa, SISC, Chibi, SCM, Chez, Vicare, Larceny, Ypsilon, Mosh, !IronScheme, STklos*, KSI†, Scheme 7†, UMB, VX*, SXM*, Spark, Dfsch†, Inlab*

All four numbers are the same and have 64-bit precision: Scheme 9*

All four numbers are the same and have 20-bit precision: Shoe

The first two numbers have 24-bit precision, the last two have 53-bit precision (IEEE double):  Racket, NexJ, Armed Bear CL, Allegro CL, Clozure CL, CMU CL, Embeddable CL, GNU CL, Steel Bank CL, Scieneer CL

The numbers have 19-bit, 24-bit, 53-bit, and 53-bit precision respectively: !LispWorks

The numbers have 17-bit, 24-bit, 53-bit, and arbitrary (at least 64-bit) precision respectively: CLISP

The numbers have 24-bit, 24-bit, 53-bit, and arbitrary precision respectively: Kawa

No inexact numbers: !SigScheme, Dream, Oaklisp, Owl Lisp

Report syntax errors or treat input as identifiers:  Bigloo, Scheme48/scsh, !TinyScheme, Dream, RScheme, BDC, XLisp, Rep, Schemik, Elk, Sizzle, !FemtoLisp

Inputs are treated as as special lexical syntax, not as numbers: Llava

== Footnotes ==

*Output is truncated

†Output is printed incorrectly


2012-12-22 10:56:48