Questions tagged [alu]
For questions related to Arithmetic Logic Units
14 questions
13 votes
6 answers
7k views
Did any CPU have a special instruction for multiplying or dividing by ten?
I recall reading about a CPU from the 90s which had, in addition to normal integer multiply and divide instructions, also had a special set of instructions for multiplying and dividing by ten. Does ...
- 283
1 vote
1 answer
219 views
74'181 missing zero flag but strange -1 (or all 1) flag, only makes sense in active-low mode?
Out of the popular but closed question 74'181 ALU why would anyone (have) use(d) these wild functions? I break out one aspect, that of a missing zero flag output. If I wanted to build a CPU with ...
- 1,387
9 votes
2 answers
1k views
74'181 ALU why would anyone (have) use(d) these wild functions? [closed]
Got myself a bunch of 74LS181, because they were cheap and they have been used in the VAX 11/780. And now I made myself a little tester breadboard where I am trying to figure this out in practice. My ...
- 1,387
14 votes
2 answers
2k views
Origin of "arithmetic" and "logical" for signed and unsigned shifts
The assembly language for many processors use the phrase "arithmetic shift" to represent the bitwise shift of a signed value, and "logical shift" for an unsigned value. The two ...
- 16.9k
24 votes
6 answers
8k views
Why did the Z80 with 4-bit ALU out-perform the fully 8-bit Intel 8080?
Looking at the development and architecture of the Z80, it appears to be a scaled-down, cost-reduced (in terms of total system cost), clone of the Intel 8080. It only used a 4-bit ALU. I assume this ...
- 62.1k
8 votes
1 answer
883 views
Were there any working computers using residue number systems?
Wikipedia says: A residue numeral system (RNS) is a numeral system representing integers by their values modulo several pairwise coprime integers called the moduli. Bit widths of each of those "...
- 22.3k
11 votes
5 answers
1k views
Which CPUs had instructions leaving data registers in an unspecified state?
When an ALU performs a floating point division operation using the non-restoring or the SRT algorithm, it maintains the current value of the "remainder" (in quotes, because it is not a true ...
- 22.3k