bug#14917: Missing range check in fxcopy-bit can give SIGABRT

["Göran Weinholt" <goran@weinholt.se>]

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Hello schemers,

the fxcopy-bit procedure from (rnrs) is missing some range checks. It
can return a non-fixnum:

scheme@(guile-user)> (import (rnrs))
scheme@(guile-user)> (fxcopy-bit 0 (fixnum-width) 1)
$1 = 9223372036854775808

It can also crash the guile process, which is somewhat surprising for a
fixnum procedure:

scheme@(guile-user)> (import (rnrs))
scheme@(guile-user)> (fxcopy-bit 0 100000000000 0)
FATAL: memory error in realloc
Aborted

Here's an alternative error message:

scheme@(guile-user)> (import (rnrs))
scheme@(guile-user)> (fxcopy-bit 0 1000000000000 0)
gmp: overflow in mpz type
Aborted

Other implementations of fxcopy-bit usually check that the third
argument is 0 or 1, but I'm not sure that is required.

There's also a bitwise-copy-bit procedure that is similary affected.
Tested with Guile 2.0.9.40-824b-dirty on an amd64 system.

Regards,

-- 
Göran Weinholt <goran@weinholt.se>
"Mr. Crane, please remember you're not required to answer any of
Lt. Tragg's questions. As a matter of fact, don't even discuss the
weather with him, he can be very persuasive." -- Perry Mason

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