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SCM_I_INUM: Rewrite to avoid unspecified behavior when not using GNU C.

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* libguile/numbers.h (SCM_I_INUM): Unless using GNU C, use a portable
  implementation that avoids unspecified behavior.
This commit is contained in:
Mark H Weaver 2014-03-11 21:33:48 -04:00
parent e293c94c65
commit 3aecd36464
1 changed files with 16 additions and 1 deletions
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17
libguile/numbers.h
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@ -65,12 +65,27 @@ typedef scm_t_int32 scm_t_wchar;
#endif #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_INUMP(x) (2 & SCM_UNPACK (x))
#define SCM_I_NINUMP(x) (!SCM_I_INUMP (x)) #define SCM_I_NINUMP(x) (!SCM_I_INUMP (x))
#define SCM_I_MAKINUM(x) \ #define SCM_I_MAKINUM(x) \
(SCM_PACK ((((scm_t_bits) (x)) << 2) + scm_tc2_int)) (SCM_PACK ((((scm_t_bits) (x)) << 2) + scm_tc2_int))
#define SCM_I_INUM(x) (SCM_SRS ((scm_t_signed_bits) SCM_UNPACK (x), 2))
/* SCM_FIXABLE is true if its long argument can be encoded in an SCM_INUM. */ /* SCM_FIXABLE is true if its long argument can be encoded in an SCM_INUM. */
#define SCM_POSFIXABLE(n) ((n) <= SCM_MOST_POSITIVE_FIXNUM) #define SCM_POSFIXABLE(n) ((n) <= SCM_MOST_POSITIVE_FIXNUM)