Scheme Programmer's Manual
bitwise-length, fxlength - bitwise length of an integer
(import (rnrs)) ;R6RS
(import (rnrs arithmetic bitwise)) ;R6RS
(import (rnrs arithmetic fixnums)) ;R6RS
Returns the number of bits needed to represent
if it is positive, and the number of bits needed to represent
(bitwise-not ei) if it is negative.
variant constrains the argument and return value to the
There are no noteworthy differences between implementations of
these procedures, apart from performance differences. R6RS gives
this standard definition:
(do ((result 0 (+ result 1))
(bits (if (negative? ei)
(bitwise-arithmetic-shift bits -1)))
This implementation runs in O(n) where n is the bitwise length of the
input. An implementation which is O(1) is possible if the implementer
has access to the internal structure of bignums. Furthermore, CPUs
often provide instructions that speed up the fixnum case.
Returns a single exact integer object.
This procedure is commonly used to compute the number bytes needed to
represent an integer during serialization to an external format.
This procedure can be implemented more efficiently by the Scheme
runtime than by portable code, and it has some use in applications.
These procedures are specified by R6RS. The generic variant is
in Common Lisp, SRFI 33, SRFI 60 and SRFI 151.
The usual compatibility concerns surrounding fixnums apply to the
This procedure can raise exceptions with the following condition types:
- &assertion (R6RS)
The wrong number of arguments was passed or an argument was outside its domain.
This page is part of the
It includes materials from the RnRS documents.
More information can be found at
Return to Main Contents
- IMPLEMENTATION NOTES
- RETURN VALUES
- APPLICATION USAGE
- SEE ALSO