On January 31, 2018 at 8:06 AM Kirk Wolf wrote:
On Tue, Jan 30, 2018 at 9:39 PM, Jon Perryman wrote:
C is a byte by byte language. Anything not hidden in a primitive or
function must be processed byte by byte. In primitives and functions, the
compiler can choose how to implement it. The point is C programmers must
process byte by byte unless they can find a function.
I'm sorry, but can't agree with anything of this.
1) Compilers can generate machine instruction implementations that take
advantage of the instructions and architecture available. Even if you
write byte-by-byte code, a compiler may rewrite it to use zArch
instructions that are not byte-by-byte but equivalent. This is distinctly
different from how assemblers work.
I think I at least somewhat understand what he means.
It occurred to me some time ago, that there is no C library
routine to do what MVCIN does. Not that it is hard to do,
but there just isn't one. I doubt many compilers compile
the appropriate for loop into MVCIN.
2) The "C Standard Library" is part of the C language standard(s). For
all of the supposed byte-by-byte C programmers that can't find any
functions to use, here are links to the XL/C++ documentation, where the
"Runtime Library Reference" can be found:
https://www-01.ibm.com/support/docview.wss?uid=swg27036892
The bottom line is that this:
memcpy(field1, field2, sizeof(field1));
generates an MVC instruction (or several or a loop or an unrolled loop of
MVC instructions).
To say that the "C Language" is byte-by-byte is pedantic.
It does. But note that C doesn't have some statements that
other languages have, that generate a lot of code from a small
statement. No array expressions, for example.
3) I also do not agree with your repeated assertion that it means
something
significant that C was originally developed on a RISC machine ( I believe
that it was a PDP-7) with only certain instructions.
The RISC/CISC idea didn't come until later. Machines like the
PDP-7 have simpler instructions to keep costs down, and make
them easier to build.
I would have thought that this kind of argument about the relative
benefits
of assemblers vs compilers (or assembler vs C) would have been over a
couple of decades ago. A more current argument is static vs dynamic
(VM+JIT) compilation.
