Calc: allow infinite binary word size (bug#43764)

Setting the word size ("b w") to 0 removes the word size clipping for
all bit operations (effectively as if a word size of -∞ had been set).
Rotation is disallowed; logical and arithmetic shifts behave
identically.

After a suggestion by Vincent Belaïche.

* lisp/calc/calc-bin.el (calc-word-size, math-binary-arg)
(math-binary-modulo-args, calcFunc-lsh, calcFunc-ash, calcFunc-rot)
(math-clip, math-format-twos-complement): Allow a word size of 0,
meaning -∞.
* test/lisp/calc/calc-tests.el
(calc-tests--not, calc-tests--and, calc-tests--or, calc-tests--xor)
(calc-tests--diff): New functions.
(calc-tests--clip, calc-tests--rot, calc-shift-binary): Extend to
cover word size 0.
(calc-bit-ops): New test.
* doc/misc/calc.texi (Binary Functions): Update manual.
* etc/NEWS: Announce the change.

1 files changed, 10 insertions, 1 deletions

diff --git a/doc/misc/calc.texi b/doc/misc/calc.texi
index a356cecf2b7..6a6f585ce20 100644
--- a/doc/misc/calc.texi
+++ b/doc/misc/calc.texi
@@ -18077,7 +18077,7 @@ zeros with @kbd{d z}.  @xref{Radix Modes}.
 
 @cindex Word size for binary operations
 The Calculator maintains a current @dfn{word size} @expr{w}, an
-arbitrary positive or negative integer.  For a positive word size, all
+arbitrary integer.  For a positive word size, all
 of the binary operations described here operate modulo @expr{2^w}.  In
 particular, negative arguments are converted to positive integers modulo
 @expr{2^w} by all binary functions.
@@ -18092,6 +18092,9 @@ to
 inclusive.  Either mode accepts inputs in any range; the sign of
 @expr{w} affects only the results produced.
 
+If the word size is zero, binary operations work on the entire number
+without clipping, as if the word size had been negative infinity.
+
 @kindex b c
 @pindex calc-clip
 @tindex clip
@@ -18221,6 +18224,10 @@ and @samp{rash} operations is totally independent from whether the word
 size is positive or negative.)  With a negative prefix argument, this
 performs a standard left shift.
 
+When the word size is zero, logical and arithmetic shift operations
+are identical: a negative value shifted right remains negative, since
+there is an infinite supply of ones to shift in.
+
 @kindex b t
 @pindex calc-rotate-binary
 @tindex rot
@@ -18230,6 +18237,8 @@ word size) is dropped off the left and shifted in on the right.  With a
 numeric prefix argument, the number is rotated that many bits to the left
 or right.
 
+Rotation is not possible with a zero word size.
+
 @xref{Set Operations}, for the @kbd{b p} and @kbd{b u} commands that
 pack and unpack binary integers into sets.  (For example, @kbd{b u}
 unpacks the number @samp{2#11001} to the set of bit-numbers