diff options
Diffstat (limited to 'libguile/numbers.h')
| -rw-r--r-- | libguile/numbers.h | 40 |
1 files changed, 32 insertions, 8 deletions
diff --git a/libguile/numbers.h b/libguile/numbers.h index 6e382ea35..bba336bd4 100644 --- a/libguile/numbers.h +++ b/libguile/numbers.h @@ -4,7 +4,7 @@ #define SCM_NUMBERS_H /* Copyright (C) 1995,1996,1998,2000,2001,2002,2003,2004,2005, 2006, - * 2008, 2009, 2010, 2011, 2013 Free Software Foundation, Inc. + * 2008, 2009, 2010, 2011, 2013, 2014 Free Software Foundation, Inc. * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public License @@ -49,19 +49,43 @@ typedef scm_t_int32 scm_t_wchar; #define SCM_MOST_POSITIVE_FIXNUM ((SCM_T_SIGNED_BITS_MAX-3)/4) #define SCM_MOST_NEGATIVE_FIXNUM (-SCM_MOST_POSITIVE_FIXNUM-1) -/* SCM_SRS is signed right shift */ -#if (-1 == (((-1) << 2) + 2) >> 2) -# define SCM_SRS(x, y) ((x) >> (y)) +/* SCM_SRS (X, Y) is signed right shift, defined as floor (X / 2^Y), + where Y must be non-negative and less than the width in bits of X. + It's common for >> to do this, but the C standards do not specify + what happens when X is negative. + + NOTE: X must not perform side effects. */ +#if (-1 >> 2 == -1) && (-4 >> 2 == -1) && (-5 >> 2 == -2) && (-8 >> 2 == -2) +# define SCM_SRS(x, y) ((x) >> (y)) #else -# define SCM_SRS(x, y) ((x) < 0 ? ~((~(x)) >> (y)) : ((x) >> (y))) -#endif /* (-1 == (((-1) << 2) + 2) >> 2) */ +# define SCM_SRS(x, y) \ + ((x) < 0 \ + ? -1 - (scm_t_signed_bits) (~(scm_t_bits)(x) >> (y)) \ + : ((x) >> (y))) +#endif + +/* The first implementation of SCM_I_INUM below depends on behavior that + is specified by GNU C but not by C standards, namely that when + casting to a signed integer of width N, the value is reduced modulo + 2^N to be within range of the type. The second implementation below + should be portable to all conforming C implementations, but may be + less efficient if the compiler is not sufficiently clever. + + NOTE: X must not perform side effects. */ +#ifdef __GNUC__ +# define SCM_I_INUM(x) (SCM_SRS ((scm_t_signed_bits) SCM_UNPACK (x), 2)) +#else +# define SCM_I_INUM(x) \ + (SCM_UNPACK (x) > LONG_MAX \ + ? -1 - (scm_t_signed_bits) (~SCM_UNPACK (x) >> 2) \ + : (scm_t_signed_bits) (SCM_UNPACK (x) >> 2)) +#endif #define SCM_I_INUMP(x) (2 & SCM_UNPACK (x)) #define SCM_I_NINUMP(x) (!SCM_I_INUMP (x)) #define SCM_I_MAKINUM(x) \ - (SCM_PACK ((((scm_t_signed_bits) (x)) << 2) + scm_tc2_int)) -#define SCM_I_INUM(x) (SCM_SRS ((scm_t_signed_bits) SCM_UNPACK (x), 2)) + (SCM_PACK ((((scm_t_bits) (x)) << 2) + scm_tc2_int)) /* SCM_FIXABLE is true if its long argument can be encoded in an SCM_INUM. */ #define SCM_POSFIXABLE(n) ((n) <= SCM_MOST_POSITIVE_FIXNUM) |