* doc/m4.texi (Eval): Mention that the shift amount of << and >> is
implicity truncated. Mention that radix > 10 can cause macro expansion.
Enhance unit tests to cover this.
---
doc/m4.texi | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/doc/m4.texi b/doc/m4.texi
index 81476bc8..5a7980e7 100644
--- a/doc/m4.texi
+++ b/doc/m4.texi
@@ -7152,7 +7152,9 @@ Eval
aware that parentheses may be required to enforce C precedence rules.
Likewise, division by zero, even in the unused branch of a
short-circuiting operator, is not always well-defined in other
-implementations.
+implementations. While GNU M4 implicitly masks the right argument
+of a shift operator to 5 bits, other implementations may have undefined
+behavior for a negative argument or a positive argument greater than 31.
Following are some examples where the current version of M4 follows C
precedence rules, but where older versions and some other
@@ -7190,6 +7192,10 @@ Eval
eval(`2 && (1 % 0)')
@error{}m4:stdin:13: warning: eval: modulo by zero: '2 && (1 % 0)'
@result{}
+`0x'eval(`0x12345678>>40', `16')
+@result{}0x123456
+`0x'eval(`0x12345678>>-8', `16')
+@result{}0x12
@end example
@cindex GNU extensions
@@ -7246,7 +7252,10 @@ Eval
for all other radices, the digits are @samp{0}, @samp{1}, @samp{2},
@dots{}. Beyond @samp{9}, the digits are @samp{a}, @samp{b} @dots{} up
to @samp{z}. Lower and upper case letters can be used interchangeably
-in numbers prefixes and as number digits.
+in numbers prefixes and as number digits. Note that when using a radix
+larger than 10, input literals may need to be quoted to avoid inadvertent
+macro expansion, and the output of @code{eval} can also trigger macro
+expansion unless coupled with @code{qindir}.
Parentheses may be used to group subexpressions whenever needed. For the
relational operators, a true relation returns @code{1}, and a false
@@ -7275,13 +7284,17 @@ Eval
@result{}676
define(`foo', `666')
@result{}
+eval(`0r36:fOo', `36')
+@result{}666
+qindir(`eval', `0r36:fOo', `36')
+@result{}foo
eval(`foo / 6')
-@error{}m4:stdin:11: warning: eval: bad input: 'foo / 6'
+@error{}m4:stdin:13: warning: eval: bad input: 'foo / 6'
@result{}
eval(foo / 6)
@result{}111
eval(`1+')
-@error{}m4:stdin:13: warning: eval: missing operand: '1+'
+@error{}m4:stdin:15: warning: eval: missing operand: '1+'
@result{}
@end example
--
2.49.0
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