## Searching a Number in an Array Address

```
CUSP Assembly Code for Binary Search
.EQU NUMBER, $100
.EQU N, $101
.EQU SORTED, $102
.EQU @,$000 ; program start address
LDS# $E00 ; initialize stack to $E00
BinSearch:
LDA# 0 ; start left index in 0
STA LEFT ; update variable
LDA N ; load number of elements in acc
SBA# 1 ; start right index in n-1 = 5
STA RIGHT ; update variable
Search: LDA LEFT ; load LEFT index value in ACC
CMA RIGHT ; see if LEFT <=RIGHT
JGT fail ; if not, end search, we didn't find the number
ADA RIGHT ; Add LEFT+RIGHT
SHRA ; divide by 2 using a shift right to get the middle
TAX ; save middle index in X
LDA NUMBER ; load number to search in ACC
CMA+ SORTED ; compare number with SORTED[middle]
JEQ found ; if they are equal, we found it
JLT setright ; if the number is < middle, adjust right index
setleft: ; else, number > middle, adjust left index
ADX# 1 ; calculate middle+1
STX LEFT ; set LEFT = middle+1
JMP Search ; search again
setright:
SBX# 1 ; calculate middle-1
STX RIGHT ; set RIGHT = middle-1
JMP Search ; search again
found:
LDA# 1 ; set acc to 1 to indicate found
JMP done ; terminate program
fail:
LDA# 0 ; set acc to 0 to indicate not found
done:
HLT
; Variables for the search:
LEFT: .WORD 0
RIGHT: .WORD 5
.END
```