doco primitive numerics C funcs

[Kevin Ryde]

        * scheme-data.texi (Primitive Numerics): Add atan2, pow, asinh, acosh
        and atanh to scheme<->C table.  Note asinh, acosh and atanh are C99,
        and scm_asinh, scm_acosh and scm_atanh are equivalents.  Cross ref
        glibc "Mathematics".  Reword this end part for clarity.

I think it's clearer to have the scheme<->C table first, then the
extra inverse-hyperbolics.

I found the bit

        except `expt' and `atan2' (whose entries specifically mention
        an equivalent C function)

a little unclear.  I thought it was saying there were C "double"
functions mentioned, where instead it's SCM functions.  I think this
can be quietly dropped now $expt<->pow and $atan2<->atan2 are in the
table.

For ease of contemplation, the end part proposed is,



   C functions for the above are provided by the standard mathematics
library.  Naturally these expect and return `double' arguments (*note
Mathematics: (libc)Mathematics.).

     Scheme Procedure   C Function
     `$abs'             `fabs'
     `$sqrt'            `sqrt'
     `$sin'             `sin'
     `$cos'             `cos'
     `$tan'             `tan'
     `$asin'            `asin'
     `$acos'            `acos'
     `$atan'            `atan'
     `$atan2'           `atan2'
     `$exp'             `exp'
     `$expt'            `pow'
     `$log'             `log'
     `$sinh'            `sinh'
     `$cosh'            `cosh'
     `$tanh'            `tanh'
     `$asinh'           `asinh'
     `$acosh'           `acosh'
     `$atanh'           `atanh'

   `asinh', `acosh' and `atanh' are C99 standard but might not be
available on older systems.  Guile provides the following equivalents
(on all systems).

 - C Function: double scm_asinh (double x)
 - C Function: double scm_acosh (double x)
 - C Function: double scm_atanh (double x)
     Return the hyperbolic arcsine, arccosine or arctangent of X
     respectively.

scheme-data.texi.primitive-numerics.diff
Description: Text document