Scheme Programmer's Manual

NAME

fixnum-width - the width of the fixnum range

LIBRARY

(import (rnrs))                     ;R6RS
(import (rnrs arithmetic fixnums))  ;R6RS

SYNOPSIS

(fixnum-width)

DESCRIPTION

The fixnum range is defined as the closed interval [−2^(w−1), 2^(w−1)−1] such that w is an implementation-defined integer w ≥ 24. This procedure returns the implementation's w.

IMPLEMENTATION NOTES

The fixnum width depends very much on implementation details and the machine. Here are some known fixnum widths.


Chez Scheme: The fixnum width is 61 or 30. If the machine's register width is m then the fixnum width is m - log2(m/8).
GNU Guile: The fixnum width is 62 or 30. This is the machine's register width minus two.
IronScheme: The fixnum width is 32.
Loko Scheme: The fixnum width is 61.

RETURN VALUES

Returns a single fixnum equal to or larger than 24.

EXAMPLES

If the fixnum width is 32 (or greater) then fixnums can represent all signed 32-bit integers.

(fixnum-width) => 61

APPLICATION USAGE

This procedure is sometimes used in libraries that provide optimized variants of code for implementations where the fixnum width is large enough.

COMPATIBILITY

This procedure is only present in R6RS. An alternative is (+ 1 (bitwise-length (greatest-fixnum))).

ERRORS

This procedure never raises an exception.

STANDARDS

R6RS

AUTHORS

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