After having reimplemented most of my C# Z80 emulator in C, I’m now trying to figure out why every ZEXALL test is failing:
james@jameslaptop:~/Projects/Emulation/ZZ80E$ ./a.out z80/zexall_sdsc.sms
Z80 instruction exerciser
ld hl,(nnnn)................. CRC:350e5018 expected:5f972487
ld sp,(nnnn)................. CRC:45f3041a expected:7acea11b
ld (nnnn),hl................. CRC:c9f9ffd8 expected:a3608b47
...etc...
My first guess was that there was a bug in one of the opcodes used to calculate the CRC because I know for sure that the ld opcodes are fine.
However after going through the list of opcodes involved in the CRC with a toothpick, I still can’t find any glaring or even minor mistakes 
The problem with emulator debugging, especially at such an early stage, is that it’s hard to tell if you’re looking in the right place; the bug might be in a seemingly unrelated piece of code, the effects of which have simply cascaded down the chain.
It’s going to be a long night.