On 2022-06-17 00:36, Schmitt, Michael wrote:
My company's COBOL coding standards are* to define binary fields as
signed (e.g. PIC S9(4) BINARY). I'm wondering why that's the standard.
The original standards were developed at least 40-60 years ago. They
were revised in 1994 but the signed binary guidance remained.
One explanation could be if 50 years ago there were only signed binary
instructions such as ADD, but not logical instructions such as ADD
LOGICAL. Or maybe there were some logical instructions but not the
full complement we have today.
Or it could be that whatever version of COBOL was used then (OS/VS
COBOL or earlier) was more efficient with signed binary, such as due
to the choices it made in instruction selection.
So my question is, roughly when did the machines get unsigned binary
instructions for halfwords and fullwords?
Computers have had instructions for signed and unsigned binary
since at least 1951. When negative values are expressed using
twos complement notation, ordinary addition will give the same
result whether the operation is signed or unsigned.
* "are" isn't the right word here, since the COBOL coding conventions
are no longer published anywhere. I only know what they are because I
was on the team that reviewed the 1994 revision, and have a copy
saved.
