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Re: macro FIXNUM_OVERFLOW_P in lisp.h is valid ?
From: |
Stefan Monnier |
Subject: |
Re: macro FIXNUM_OVERFLOW_P in lisp.h is valid ? |
Date: |
Fri, 23 Oct 2009 17:14:26 -0400 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.1.50 (gnu/linux) |
> I read the code of function `string-to-number', and traced functions or
> macros recursively.
> traces of string-to-number:
> data.c: Fstring_to_number
> lisp.h: make_fixnum_or_float
> lisp.h: FIXNUM_OVERFLOW_P
> citation of FIXNUM_OVERFLOW_P (in Emacs 23.1):
> /* Value is non-zero if C integer I doesn't fit into a Lisp fixnum. */
> #define FIXNUM_OVERFLOW_P(i) \
> ((EMACS_INT)(i) > MOST_POSITIVE_FIXNUM \
> || (EMACS_INT) (i) < MOST_NEGATIVE_FIXNUM)
> I think FIXNUM_OVERFLOW_P is problematic.
> The reason is that
> in case `i' is 4294967296.0 (2^32), (EMACS_INT)(i) returns 0
> with a executable program by some compiler
> (for example, Microsoft 32-bit C/C++ Compiler).
> As a result, FIXNUM_OVERFLOW_P(i) returns 0.
> In Microsoft 32-bit C/C++ Compiler:
> i (int)(i)
> ===============================================
> 2147483648.0 (2^31) -2147483648
> 2147483647.0 (2^31 - 1) 2147483647
> 4294967296.0 (2^32) 0
> 4294967295.0 (2^32 - 1) -1
> 8589934592.0 (2^33) 0
> 8589934591.0 (2^33 - 1) -1
> In gcc version 3.4.4 (cygming special):
> i (int)(i)
> ===============================================
> 2147483648.0 (2^31) -2147483648
> 2147483647.0 (2^31 - 1) 2147483647
> 4294967296.0 (2^32) -2147483648
> 4294967295.0 (2^32 - 1) -2147483648
> 8589934592.0 (2^33) -2147483648
> 8589934591.0 (2^33 - 1) -2147483648
> In conclusion, it needs casting to double, I think.
> #define FIXNUM_OVERFLOW_P(i) \
> ((double)(i) > (double)MOST_POSITIVE_FIXNUM \
> || (double)(i) < (double)MOST_NEGATIVE_FIXNUM)
> What do you think about it ?
I think the problem is that FIXNUM_OVERFLOW_P is written to handle an
integer argument, not a float argument. So rather than patch it to use
floats, I'd rather write a new macro that works for floats (and only
casts the MOST_POSITIVE_FIXNUM side).
Stefan
Re: macro FIXNUM_OVERFLOW_P in lisp.h is valid ?, Andreas Schwab, 2009/10/23
Re: macro FIXNUM_OVERFLOW_P in lisp.h is valid ?,
Stefan Monnier <=