Re: [PATCH] First batch of numerics changes

[Andy Wingo <wingo@pobox.com>]

Hi Mark,

On Wed 26 Jan 2011 17:32, Mark H Weaver <mhw@netris.org> writes:

I don't understand this change:

> From c42d03050ea0f96556e73e405e530b78bb85aba7 Mon Sep 17 00:00:00 2001
> From: Mark H Weaver <mhw@netris.org>
> Date: Wed, 26 Jan 2011 02:56:20 -0500
> Subject: [PATCH] Add case for fractions with differing SCM_CELL_TYPE to scm_equal_p
>
> * libguile/eq.c (scm_equal_p): Add a special case for fractions with
>   differing SCM_CELL_TYPE, which might nonetheless be considered equal
>   (due to the use of 0x10000 as a flag), to scm_equal_p.  This code
>   was already present in scm_eqv_p.
>
>   (scm_eqv_p): Move comment (regarding special case for fractions)
>   next to the corresponding code.
> ---
>  libguile/eq.c |   19 +++++++++++++------
>  1 files changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/libguile/eq.c b/libguile/eq.c
> index 7502559..dc548b8 100644
> @@ -322,6 +322,13 @@ scm_equal_p (SCM x, SCM y)
>  			     && SCM_COMPLEX_IMAG (x) == 0.0);
>  	}
>  
> +      /* fractions use 0x10000 as a flag (at the suggestion of Marius Vollmer),
> +	 but this checks the entire type word, so fractions may be accidentally
> +	 flagged here as unequal.  Perhaps I should use the 4th double_cell word?
> +      */
> +      if (SCM_FRACTIONP (x) && SCM_FRACTIONP (y))
> +	return scm_i_fraction_equalp (x, y);
> +
>        /* Vectors can be equal to one-dimensional arrays.
>         */
>        if (scm_is_array (x) && scm_is_array (y))

In what case would two fractions ever not have the same SCM_CELL_TYPE ?
I don't understand this discussion of flags.  AFAICS fractions have their
own tc16, and no flags are ever set.

Furthermore I would think that the `if (SCM_NUMP (x))' block in
scm_eqv_p could use a switch statement instead of a bunch of ifs.

Regards,

Andy
-- 
http://wingolog.org/