Sigbjorn
Am confused by your answer.
| > char fooble ( ... )
| > {
| > return 'z';
| > }
| >
| > on an x86, 'z' will be returned at the lowest 8 bits in %eax. What I
| > don't know is, is the C compiler obliged to clear the upper 24 bits
of
| > %eax, or does that onus fall on the callee?
|
| Yes, the callee is required to narrow <expr> in 'return
| <expr>;' to fit that of the specified return type -- see 9.8
| of Harbison and Steele. So, a C compiler that cause f() to
| return 0x7fffffff for the following,
|
| unsigned char g()
| {
| return 0x7fffffff;
| }
|
| unsigned int f()
| {
| return g();
| }
|
| is in the wrong. [Notice that narrowing for signed integral
| types is undefined in ISO C, but most current-day compilers
| implement such narrowing ops the same way, i.e., by masking
| off excess bits.]
So we don't need to worry about doing the masking on the
Haskell side, right?
| > Also, I don't even know where to look for the specification
| of details
| > of the C calling conventions. Anyone got a clue?
| >
|
| Harbison & Steele Chapters 6 and 9 cover the conversion rules
| that apply to functions (and other expressions). As you no
| doubt already know, lower-level details are the domain of a
| platform's ABI.
|
| Sounds to me like unboxed sized Words and Ints is the
| (unavoidable) way to go.
Why would we need these unless we *did* need to worry about
masking on the Haskell side?
Pls clarify.
J
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