dinoxor.s
1 .global _dinoxor 2 .text 3 4 // Function: dinoxor 5 // Description: Orchestrates a series of operations to replicate a bitwise XOR 6 // operation using NEON registers. This function initializes a XOR truth table, 7 // calculates an index based on provided Xindex and Yindex, and creates a 8 // multiplication table to help calculate the index of each byte into the truth table. 9 // Arguments: 10 // - x0: First operand byte 11 // - x1: Second operand byte 12 // Returns: The result of the XOR operation between the two input bytes in w0. 13 _dinoxor: 14 // Prologue: Prepare the stack and save callee-saved registers 15 stp x29, x30, [sp, #-16]! // Save the frame pointer and return address on the stack 16 mov x29, sp // Update the frame pointer to the current stack pointer 17 18 mov x2, #0 // Initialize x2 to 0 (not used later) 19 eor v0.16b, v0.16b, v0.16b // Clear the contents of v0 (set all bits to 0) 20 21 bl spread_bits_to_bytes // Call the spread_bits_to_bytes function to load the first operand byte into the lower half of v2 22 mov x0, x1 // Move the second operand byte into x0 23 bl spread_bits_to_bytes // Call the spread_bits_to_bytes function to load the second operand byte into the lower half of v2 (shifting the previous value to upper) 24 // After the above operations 25 // For the inputs: 26 // x0 = 0b10101010 27 // x1 = 0b11111111 28 // v2 contains: 29 // v2 = {0x00 0x01 0x00 0x01 0x00 0x01 0x00 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01} 30 31 bl prepare_xor_truth_table // Call the prepare_xor_truth_table function to initialize the XOR truth table in v0 32 // After the above operation, v0 contains: 33 // v0 = {0x00 0x01 0x01 0x00 0x00 0x01 0x01 0x00 0x00 0x01 0x01 0x00 0x00 0x01 0x01 0x00} 34 35 bl prepare_multiplication_table // Call the prepare_multiplication_table function to initialize the multiplication table in v1 36 // After the above operation, v1 contains: 37 // v1 = {0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01} 38 39 bl calculate_xor_result // Call the calculate_xor_result function to calculate and store the XOR'd byte in w0. 40 41 // Epilogue: Restore the stack and callee-saved registers 42 ldp x29, x30, [sp], #16 // Restore the frame pointer and return address from the stack 43 44 ret // Return to the caller 45 46 // Function: spread_bits_to_bytes 47 // Description: Spreads the bits of a byte into separate bytes in a NEON register. 48 // Arguments: 49 // - x0: The input byte to be spread 50 // Returns: None (the result is stored in v2) 51 spread_bits_to_bytes: 52 // Clear the destination vector registers 53 eor v1.16b, v1.16b, v1.16b 54 eor v2.16b, v2.16b, v2.16b 55 56 mov w2, #0 // Initialize the counter for bit positions (0-7) 57 58 spread_bit_loop: 59 lsr w3, w0, w2 // Shift the input byte right by the current bit position to bring the target bit to the LSB 60 and w3, w3, #0x01 // Isolate the LSB (which is now the target bit) 61 62 mov w4, w3 // Move the processed bit to w4 (to ensure w4 is correctly updated before duplication) 63 64 ext v2.16b, v0.16b, v0.16b, #1 // Shift v0 left by one byte to make space for the new byte 65 ins v2.b[0], w4 // Insert the new byte at position 0 of v2 66 mov v0.16b, v2.16b // Move the temporary result back to v0 67 68 add w2, w2, #1 // Increment the bit position counter 69 cmp w2, #8 // Compare the counter with 8 (number of bits in a byte) 70 b.lt spread_bit_loop // If the counter is less than 8, continue the loop 71 72 ext v2.16b, v0.16b, v0.16b, #1 // Shift the last byte inserted into its final position in v2 73 74 ret 75 76 // Function: prepare_xor_truth_table 77 // Description: Prepares the XOR truth table in a NEON register. 78 // Arguments: None 79 // Returns: None (the truth table is stored in v0) 80 prepare_xor_truth_table: 81 // Load a pattern into a general-purpose register 82 movz w8, #0x0001, lsl #16 // Load 0x0001 into the upper half of w8 (bits 16-31) 83 movk w8, #0x0100 // Overlay 0x0100 into the lower half of w8 (bits 0-15) 84 85 dup v0.4s, w8 // Duplicate the 32-bit value in w8 across all lanes of v0 86 // After the above operation, v0 contains: 87 // v0 = {0x00 0x01 0x01 0x00 0x00 0x01 0x01 0x00 0x00 0x01 0x01 0x00 0x00 0x01 0x01 0x00} 88 89 ret 90 91 // Function: prepare_multiplication_table 92 // Description: Sets up a multiplication table in v1 to help calculate the index of each byte into the truth table. 93 // Arguments: None 94 // Returns: None (the multiplication table is stored in v1) 95 prepare_multiplication_table: 96 // Load the patterns into NEON registers 97 movi v1.8b, #0x02 // Set the lower half of v1 to 0x02 98 movi v8.8b, #0x01 // Set the lower half of v8 to 0x01 99 100 mov v1.d[1], v8.d[0] // Move the lower half of v8 to the upper half of v1 101 // After the above operations, v1 contains: 102 // v1 = {0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x02 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01} 103 104 ret 105 106 // Function: calculate_xor_result 107 // Description: Calculates the XOR result using the prepared data in NEON registers. 108 // It multiplies the spread bits by the multiplication table to get the indices, 109 // performs a table lookup using the XOR truth table, and then multiplies the result 110 // by a predefined pattern to obtain the final XOR result. 111 // Arguments: 112 // - v0: The XOR truth table 113 // - v1: The multiplication table 114 // - v2: The spread bits of the input operands 115 // Returns: The XOR result of the input operands in w0 116 calculate_xor_result: 117 mul v3.16b, v2.16b, v1.16b // Multiply each byte in v2 (spread bits) by its corresponding byte in v1 (multiplication table) 118 // The upper half of v3 now contains the relevant Xindexes 119 mov v3.d[1], v2.d[1] // Move the upper half of v2 (Yindexes) to the lower half of v3 120 ext.16b v1, v3, v3, #8 // Extract the upper half of v3 and store it in v1 121 add.16b v1, v3, v1 // Add v3 and v1 to get the final indices for the truth table lookup 122 mov.d v1[1], xzr // Clear the upper half of v1 (set it to 0) 123 tbl.8b v1, {v0}, v1 // Perform a table lookup using the indices in v1 and the truth table in v0 124 // Store the result in v1 125 126 // Set up v0 with the desired values for the multiplication 127 movz x1, #0x0201, lsl #0 // Load the lower 16 bits of x1 with 0x0201 128 movk x1, #0x0804, lsl #16 // Load the next 16 bits of x1 with 0x0804 129 movk x1, #0x2010, lsl #32 // Load the next 16 bits of x1 with 0x2010 130 movk x1, #0x8040, lsl #48 // Load the upper 16 bits of x1 with 0x8040 131 mov v0.d[0], x1 // Move the 64-bit value from x1 to the lower half of v0 132 133 mul v1.16b, v1.16b, v0.16b // Multiply v1 (table lookup result) by v0 (predefined pattern) element-wise 134 addv b0, v1.8b // Sum the values in the lower half of v1 and store the result in b0 135 umov w0, v0.b[0] // Move the 8-bit scalar value from b0 to w0 (return value) 136 137 ret