Re: mixed-sign arithmetic and auto
Walter Bright wrote:
Note that these are not ancient "nutburger" architectures -- these are
both current and in _wide_ use. Just for an obvious example, the last
time I was in Costco, they had a brand new HD-DVD player that (on the
outside of the box!) bragged about using a SHARC processor.
Here's the C++ compiler for the sharc:
http://www.analog.com/UploadedFiles/Associated_Docs/75285036450_SHARC_cc_man.pdf
I'd like to expand on this issue a bit. The C++ sharc compiler has:
1) 32 bit shorts
2) 32 bit chars
3) 40 bit doubles
While this is legal for a C++ compiler, and arbitrary C++ code may
compile successfully, that doesn't at all mean it will run. For example,
take zlib, the open source compression library, that's been ported to
many platforms. What are the odds that is going to work out of the box
with this compiler? I'd say, zero. You're going to have to redesign
large sections of it.
For example, let's look at shorts. The only reason people use shorts
these days is:
1) to reduce memory consumption
2) to manipulate 16 bit values in an existing data structure
3) to specifically use 16 bit math
4) to manipulate 2 bytes at once
because shorts are often slower than ints. So, any code using shorts for
2..4 will have to be recoded.
Similar reasoning applies to chars. Chars are very often used, not to
store characters, but to do byte manipulation. You cannot do byte
addressing on the sharc. All the C++ code you wrote to do byte
manipulation will need to be thoroughly re-engineered.
Let's look at a hypothetical D compiler for the sharc. A straightforward
implementation would probably simply make chars and shorts illegal. Code
that uses characters could be edited to use dchars instead (D's 32 bit
character type). Code that manipulates bytes and 16 bit values is going
to have to be re-engineered, just like the C++ code will be. The only
real difference to the programmer is that the D compiler will *tell* you
you cannot use chars or shorts, while the C++ compiler will compile it
anyway and produce code that won't work properly, leaving you to find it
with a debugger.
The 40 bit doubles are a bit more problematic. I'd recommend for D to
just go with 40 bit doubles on that platform, and then let the user deal
with the possible precision problems just as he would have to with C++.
The bottom line is, which language would be more work for the sharc
programmer to port code to? Only experience can tell for sure, but I
suspect D would come out ahead as the compiler will flag code that won't
work on sharc, while C++ will compile it anyway and leave it at the
mercy of his test suite to find the problems.
--------
Walter Bright
http://www.digitalmars.com
C, C++, D programming language compilers
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