Bytevector VM ops

[Ludovic Courtès]

Hello,

I'm finally looking into these new VM ops...

"Andy Wingo" <address@hidden> writes:

> +#define BV_FIXABLE_INT_REF(stem, fn_stem, type, size)                   \
> +{                                                                       \
> +  long i;                                                               \
> +  ARGS2 (bv, idx);                                                      \
> +  VM_VALIDATE_BYTEVECTOR (bv);                                          \
> +  if (SCM_LIKELY (SCM_I_INUMP (idx)                                     \
> +                  && ((i = SCM_I_INUM (idx)) >= 0)                        \
> +                  && (i < SCM_BYTEVECTOR_LENGTH (bv))                   \
> +                  && (i % size == 0)))                                  \
> +    RETURN (SCM_I_MAKINUM (*(scm_t_##type*)                             \
> +                           (SCM_BYTEVECTOR_CONTENTS (bv) + i)));        \

Did you test this on SPARC or some such?  I'm 90% sure
`(bv-u32-ref bv 1)' would lead to SIGBUS there, due to the unaligned access.
This is why `INTEGER_REF ()' in `bytevectors.c' uses memcpy(3).

> +  else                                                                  \
> +    RETURN (scm_bytevector_##fn_stem##_ref (bv, idx));                  \

In this case, we pay the overhead twice (type-checking et al.).

Given that there's some duplication with `bytevectors.c', maybe we could
share some of the accessor macros between both files?

Thanks,
Ludo'.