85 lines
No EOL
4.3 KiB
NASM
85 lines
No EOL
4.3 KiB
NASM
; ========================================================================================
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; array_reversal.asm - Array Reversal Using Swap Algorithm
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; ========================================================================================
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; This program demonstrates how to reverse an array in-place using a swap algorithm.
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; The algorithm uses two pointers - one starting from the beginning and one from the end
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; of the array. Elements are swapped in each iteration, and the pointers move towards
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; the center until they meet or cross each other.
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AREA RESET, DATA, READONLY ; Define a read-only data section for the vector table
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EXPORT __Vectors ; Export the vector table for external linking
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__Vectors ; Start of the vector table
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DCD 0x10001000 ; Stack pointer initial value (points to top of stack)
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DCD Reset_Handler ; Address of the reset handler (program entry point)
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ALIGN ; Ensure proper alignment for the next section
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AREA mycode,CODE,READONLY ; Define the code section as read-only
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ENTRY ; Mark the entry point of the program
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EXPORT Reset_Handler ; Export the reset handler function
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; ========================================================================================
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; Reset_Handler - Main program execution
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; ========================================================================================
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; Algorithm Overview:
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; 1. Initialize counter R2 to half the array size (5 iterations for 10 elements)
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; 2. Set R0 to point to the start of the array (SRC)
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; 3. Set R1 to point to the end of the array (SRC + 36 bytes = last element)
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; 4. In each iteration:
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; a. Load element from start pointer (R0) into R3
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; b. Load element from end pointer (R1) into R4
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; c. Store R3 to end pointer location and decrement R1 by 4 bytes
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; d. Store R4 to start pointer location and increment R0 by 4 bytes
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; e. Decrement counter and repeat until counter reaches zero
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Reset_Handler
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; Step 1: Initialize loop counter
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; Set R2 to 5 (half of array size 10) - number of swap operations needed
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MOV R2, #5 ; R2 = 5 (loop counter for 5 swap operations)
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; Step 2: Initialize array pointers
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; R0 points to the beginning of the array
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LDR R0, =SRC ; R0 = address of first element in SRC array
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; R1 points to the end of the array (SRC + 36 bytes)
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; 36 = 9 * 4 bytes (offset to reach the last element from first)
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LDR R1, =SRC + 36 ; R1 = address of last element in SRC array
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; Step 3: Main reversal loop
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Loop
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; Load the element from the start of array into R3
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LDR R3, [R0] ; R3 = element at current start position
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; Load the element from the end of array into R4
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LDR R4, [R1] ; R4 = element at current end position
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; Swap: Store start element (R3) to end position
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; Use post-decrement addressing: store R3 to [R1], then R1 = R1 - 4
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STR R3, [R1], #-4 ; Store R3 to end position and move pointer left
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; Swap: Store end element (R4) to start position
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; Use post-increment addressing: store R4 to [R0], then R0 = R0 + 4
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STR R4, [R0], #4 ; Store R4 to start position and move pointer right
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; Decrement loop counter
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SUBS R2, #1 ; R2 = R2 - 1 (set flags for branch condition)
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; Continue loop if counter is not zero
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BNE Loop ; Branch to Loop if R2 != 0
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; Step 4: Program termination
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; Create an infinite loop to stop program execution
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STOP
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B STOP ; Branch to STOP label (infinite loop)
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AREA mydate, DATA, READWRITE ; Define a read-write data section
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; ========================================================================================
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; Data Section - Source Array
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; ========================================================================================
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; SRC array contains 10 elements (40 bytes total):
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; Each element is a 32-bit word in hexadecimal format
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; Original array: [32, 12345644, 05, 98, AB, CD, 55, 32, CA, 45]
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; After reversal: [45, CA, 32, 55, CD, AB, 98, 05, 12345644, 32]
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SRC DCD 0x00000032, 0x12345644, 0x00000005, 0x00000098, 0x000000AB, 0x000000CD, 0x00000055, 0x00000032, 0x000000CA, 0x00000045
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END ; End of the assembly program |