[Devel] FT_PtrDist is badly defined and should be abolished

[Graham Asher]

Dear FreeTypers,

[sending this yet again in because of apparent mail problems, and copying to
Werner as a last resort]

I believe the macro FT_PtrDist should be changed or, more usefully,
abolished. It is described in a comment in fttypes.h as

"the largest _signed_ integer type used to express the distance between two
pointers"

but the definition is

typedef size_t  FT_PtrDist

and size_t is unsigned for many compilers. And ptrdiff_t is always signed in
C, because negative pointer differences are both valid and useful. This
leads to no actual problems in the operation of the code, but is illogical
and causes a compiler warning when compiling the Type1 driver for ARM using
one variant of the CodeWarrior compiler:

"src\type1\t1load.c", line 429: Warning: C2897E: odd unsigned comparison
with 0: '<='

(The code that caused this - is FT_PtrDist less than zero? - has since been
fixed, but only by changing the comparison from "len <= 0" to "len == 0",
which reduces the strength of the check and doesn't catch negative pointer
difference any more than the previous code did.)

FT_PtrDist is used only by the psaux and type 1 modules. It will do no harm
to abolish it and replace it with a long integer, because in every case it
is used somewhere that a "long" is appropriate. If preferred, it should be
replaced by

typedef long FT_PtrDist

It is inconceivable that this code would ever have to handle pointer
distances unrepresentable by a "long".

FT_Offset looks like another good candidate for abolition. Macros like this
add no value and serve merely to make the code harder to read.

Best wishes,

Graham Asher