How to compare two signed numbers in Z80 assembly?

How to compare two signed numbers in Z80 assembly?

The CP instruction subtracts -4 from 3 as follows: As you can see the carry flag is set indicating that -4 is greater than 3. Which is not what I expect = ( This makes me suspect that the logic in the quote only works for unsigned comparisons. How do you compare two signed numbers in z80 assembly?

How to compare two numbers in x86 assembler?

It varies from assembler to assembler. Most machines offer registers, which have symbolic names like R1, or EAX (the Intel x86), and have instruction names like “CMP” for compare. And for a compare instruction, you need another operand, sometimes a register, sometimes a literal. Often assemblers allow comments to the right of instruction.

Which is the lowest assembler works with bytes or bits?

The lowest assembler works with is bytes, not bits (directly anyway). If you want to know about bit logic you’ll need to take a look at circuit design.

How to compare-4 and 3 in Assembly?

Suppose I want to compare -4 and 3. According to the quote above, a less than condition is indicated with the zero flag being clear and the carry flag being clear The CP instruction subtracts -4 from 3 as follows: As you can see the carry flag is set indicating that -4 is greater than 3.

How does the Z80 instruction set differ from the 8080?

Similarly, both have a single opcode LD HL, (nn) and LD (nn),HL while only the Z-80 has the redundant ED version of LD HL, (nn) and LD (nn),HL. The Z-80 does not have a new JP instruction that tests the overflow flag. This remains the conditional jump based on parity but the “parity” bit is set based on overflow for arithmetic instructions.

How many flags need to be checked on a Z80?

On a Z80 (or any 8080 follow up) 1 to 3 flags need to be checked, depending on the question asked the resulting jumps may be rather complex. Now, drawing this up as a table gives additional insight Looking at the first 4 lines looks quite like an XOR operation, doesn’t it?

How many bits does a Z80 Number Cruncher need?

The 32 bits IEEE 754 format is expanded to a 40 bits Z80 format. The suppressed mantissa bit 2 0 is restored to 1 for normalized numbers and 0 for denormalized numbers. Left to the decimal point one more bit is added. This bit is needed for addition and subtraction.