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Assembly Language Programming(6) MOVGE

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MOVEGE Instruction in ARM Assembly

MOVGE is a conditional move instruction in ARM assembly. It stands for:

MOVGE  →  MOVE if Greater than or Equal

  • MOVGE Rd, Rn moves the value of Rn into Rd only if the condition "Greater than or Equal (GE)" is met.

  • It is a conditional execution instruction, meaning it depends on the flags in the CPSR (Current Program Status Register).

  • The GE (Greater than or Equal) condition is determined based on signed comparisons.

✅ How Does MOVGE Work?

MOVGE is executed only if the N (Negative) flag and V (Overflow) flag in CPSR are either both set or both cleared:

Condition for GE:  (N == V)

  • Signed comparison (CMP instruction) affects the N and V flags.

  • If N == V, it means the result is greater than or equal to zero in signed arithmetic.

✅ Example 1: Using MOVGE with CMP

.global _start
_start:
    MOV R0, #5      ; Load R0 with 5
    MOV R1, #3      ; Load R1 with 3
    CMP R0, R1      ; Compare R0 - R1 (5 - 3)
    MOVGE R2, R0    ; If R0 >= R1 (GE condition), move R0 to R2

Execution Steps

  1. R0 = 5, R1 = 3

  2. CMP R0, R1 → 5 - 3 = 2 (positive result)

    • N flag = 0, V flag = 0 (N == V → GE condition met)

  3. MOVGE R2, R0 executes → R2 = 5.

✅ Example 2: MOVGE when Condition Fails

.global _start
_start:
    MOV R0, #2      ; Load R0 with 2
    MOV R1, #5      ; Load R1 with 5
    CMP R0, R1      ; Compare R0 - R1 (2 - 5)
    MOVGE R2, R0    ; If R0 >= R1, move R0 to R2 (otherwise, do nothing)

Execution Steps

  1. R0 = 2, R1 = 5

  2. CMP R0, R1 → 2 - 5 = -3 (negative result)

    • N flag = 1, V flag = 0 (N ≠ V → GE condition NOT met)

  3. MOVGE R2, R0 does NOT execute → R2 remains unchanged.

✅ Summary

  • MOVGE moves a value only if R0 >= R1 (signed comparison).

  • It is affected by CPSR flags (N and V).

  • MOVGE executes when N == V, meaning the result is non-negative in signed arithmetic.

  • If the condition is false, MOVGE is skipped (does nothing).

Thus, MOVGE is useful for conditionally setting values based on signed comparisons without needing a separate branch (BGE). 🚀

assembly language