CLD and STD: clear and set the direction flag For reading and writing the sign, zero, auxiliary carry, parity, and carry flags, you can use LAHF to load the lower 8 bits (those 5 flags plus 3 indeterminate bits) into the AH register, and you can use SAHF to store those values from AH back into the flags register.
In Microsoft visual studio 2017, I wanted to check the current status of the register flags. I wanted to know what each register flag abbreviation stands for, so I checkout the wiki page on x86 register flags. But as you can see, the register flag abbreviations shown in Visual studio do not match the abbreviations in the wiki page.
0 My book and most sources show that when the carry flag is changed from 0 to 1, but i dont understand why the EFL register changes values in much bigger increments as show below: i put comments showing the change to the register value. like when moving from 0 to 1 to back to 0 to -1.
Understanding of the EFLAGS register in x86, going from 1 to 0 to -1 ...
Adding 0FFh and 05h in an 8-bit register does not set the Overflow flag. (the answer is 300 so how is there not an overflow flag on? It’s above 256) Again, overflow is signed overflow. This causes an unsigned overflow, so the carry bit will be set. Adding 5 to 0FBh in an 8-bit register sets the Zero flag (The answer here is 256, not 0.
This maybe the case of the XY problem. To check for overflow you do not need to get the hardware overflow flag as you think because the flag can be calculated easily from the sign bits An illustrative example is what happens if we add 127 and 127 using 8-bit registers. 127+127 is 254, but using 8-bit arithmetic the result would be 1111 1110 binary, which is -2 in two's complement, and thus ...