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(Bitwise Operations): In logtest and logbit?, describe

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operations in words, not just equivalent expressions.  In
integer-expt, clarify a bit and note negative k allowed and 0^0==1.
This commit is contained in:
Kevin Ryde 2005-01-14 23:20:25 +00:00
parent 0b5a0521d1
commit a46648acb3
1 changed files with 19 additions and 12 deletions
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31
doc/ref/api-data.texi
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@ -1493,9 +1493,11 @@ argument, ie.@: each 0 bit is changed to 1 and each 1 bit to 0.
@deffn {Scheme Procedure} logtest j k
@deffnx {C Function} scm_logtest (j, k)
@lisp
(logtest j k) @equiv{} (not (zero? (logand j k)))
Test whether @var{j} and @var{k} have any 1 bits in common. This is
equivalent to @code{(not (zero? (logand j k)))}, but without actually
calculating the @code{logand}, just testing for non-zero.
@lisp
(logtest #b0100 #b1011) @result{} #f
(logtest #b0100 #b0111) @result{} #t
@end lisp
@ -1503,9 +1505,10 @@ argument, ie.@: each 0 bit is changed to 1 and each 1 bit to 0.
@deffn {Scheme Procedure} logbit? index j
@deffnx {C Function} scm_logbit_p (index, j)
@lisp
(logbit? index j) @equiv{} (logtest (integer-expt 2 index) j)
Test whether bit number @var{index} in @var{j} is set. @var{index}
starts from 0 for the least significant bit.
@lisp
(logbit? 0 #b1101) @result{} #t
(logbit? 1 #b1101) @result{} #f
(logbit? 2 #b1101) @result{} #t
@ -1539,10 +1542,10 @@ dropping bits.
@deffn {Scheme Procedure} logcount n
@deffnx {C Function} scm_logcount (n)
Return the number of bits in integer @var{n}. If integer is
Return the number of bits in integer @var{n}. If @var{n} is
positive, the 1-bits in its binary representation are counted.
If negative, the 0-bits in its two's-complement binary
representation are counted. If 0, 0 is returned.
representation are counted. If zero, 0 is returned.
@lisp
(logcount #b10101010)
@ -1574,14 +1577,18 @@ zero bit in twos complement form.
@deffn {Scheme Procedure} integer-expt n k
@deffnx {C Function} scm_integer_expt (n, k)
Return @var{n} raised to the exact integer exponent
@var{k}.
Return @var{n} raised to the power @var{k}. @var{k} must be an exact
integer, @var{n} can be any number.
Negative @var{k} is supported, and results in @m{1/n^|k|, 1/n^abs(k)}
in the usual way. @math{@var{n}^0} is 1, as usual, and that includes
@math{0^0} is 1.
@lisp
(integer-expt 2 5)
@result{} 32
(integer-expt -3 3)
@result{} -27
(integer-expt 2 5) @result{} 32
(integer-expt -3 3) @result{} -27
(integer-expt 5 -3) @result{} 1/125
(integer-expt 0 0) @result{} 1
@end lisp
@end deffn