Unexpected srfi-4 C Interface Change in 2.0.10

[Daniel Llorens]

> Message: 2
> Date: Wed, 19 Mar 2014 10:22:40 -0400
> From: Barry Fishman <address@hidden>
> To: address@hidden
> Subject: Unexpected srfi-4 C Interface Change in 2.0.10
> Message-ID: <address@hidden>
> Content-Type: text/plain
> 
> When building C interface code using scm_f32vector_writable_elements()
> in 2.0.10 and on the trunk I found:
> 
> For a vector generated in guile with:
> 
>  (f32vector 0.25 0.25 0.25 1.0)
> 
> I found in the C interface:
> 
>  scm_t_array_handle handle;
>  size_t vlen, vinc;
>  float *arrayp;
> 
>  arrayp = scm_f32vector_writable_elements(s_uvec, &handle,
>                                           &vlen, &vinc)
> 
> When I test vlen it now seems to contain the number of bytes (16)
> rather than the number of elements (4) in the f32vector.
> 
> It was 4 in 2.0.9 and the guile trunk I built on Jan 8.
> It was 16 in 2.0.10 and the guile trunk I built on March 17.
> I assume it relates to the Feb 8 changes, where:
> (in commit dc65b88d839c326889618112c4870ad3a64e9446)
> 
>    *lenp = scm_c_bytevector_length (uvec) / width;
> 
> and width is set to 1 in the macro:
> 
> DEFINE_SRFI_4_C_FUNCS (F32, f32, float, 1);

This is a bug. Is there a test setup for the C interface?

The last argument of DEFINE_SRFI_4_C_FUNCS (1) is correct; that can be 1 or 2, 
because complex types use a pointer to real. We could use C99 complex types and 
get rid of it. Just cast the pointer for C<99 users (?)

The bug appeared in replacing the deprecated scm_uniform_vector_elements() with 
the bytevector functions. Generally lengths are computed with 
scm_i_array_element_type_sizes[] in uniform.c (e.g. see make_bytevector() in 
bytevector.c).

So the patch would be

   *lenp = scm_c_bytevector_length (uvec) / (width * 
scm_i_array_element_type_sizes[ETYPE (TAG)]) ;

Actually I'd do

   *lenp = scm_c_bytevector_length (uvec) / (width * sizeof(ctype))

(Both untested).

Regards,

        Daniel