CPIR - Z80 instruction reference

cpirCompare, increment and repeat 
Repeats CPI, scanning up memory from HL for a byte equal to A, until a match is found or BC is zero.
2 bytes · 21/16 cycles·21 cycles for a pass that repeats, 16 for the last
SZHP/VNC ●●●●1–
● set from the result
1 always 1
– not changed
Forms  cpir  
Compares the value of the memory location pointed to by HL with A. Then HL is incremented and BC is decremented. If BC is not zero and z is not set, this operation is repeated. p/v is reset if BC becomes zero and set otherwise, acting as an indicator that HL reached a memory location whose value equalled A before the counter went to zero. Interrupts can trigger while this instruction is processing.
         .org 0x8000
        ld a, 3
        ld hl, source
        ld bc, 4
        cpir
        halt
source: .byte 1, 2, 3, 4