Game Boy: What constitutes a “half-carry”?

Question

The Game Boy Z80 CPU has a half-carry flag, and I can\'t seem to find much information about when to set/clear it.

What I understand so far is that any 8-bit add, su

Answer 1

Since the half-carry flag is one of the most common stumbling blocks for Game Boy emulator makers, I'll take the liberty to post a link to a recent question of mine regarding the subject as an answer:

Game Boy: Half-carry flag and 16-bit instructions (especially opcode 0xE8)

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A summary of the above thread (answer by @gekkio):

It depends on the instruction, but the flags are always updated based on the same bit positions if you think in terms of 8-bit values...it just varies whether we're talking about the high or low byte of the 16-bit value. Bit 11 is just bit 3 of the high byte.

• ADD SP, e: H from bit 3, C from bit 7 (flags from low byte op)
• LD HL, SP+e: H from bit 3, C from bit 7 (flags from low byte op)
• ADD HL, rr: H from bit 11, C from bit 15 (flags from high byte op)
• INC rr: no flag updates (executed by the 16-bit inc/dec unit)
• DEC rr: no flag updates (executed by the 16-bit inc/dec unit)