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testing_partition.txt

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+main:	lda x4, start
+	ldur x0, [x4, #0]
+	bl FindTail
+	addi x2, x1, #24
+	stur x2, [sp, #0]
+	bl Partition
+	STOP
+
+
+FindTail:
+	SUBI SP, SP, #64
+	STUR FP, [SP, #0]
+	ADDI FP, SP, #56
+	STUR LR, [SP, #8]
+	//ADD X1, X1, X0 // x1 = x0
+
+if_tail: 
+	LDUR X9, [X0, #16] // *(pt + 2)
+	ADDIS XZR, X9, #1 // *(pt + 2) = -1
+	B.EQ rettail
+else_tail:
+	//STUR X0, [SP, #16] // backup X0
+	ADDI X0, X0, #16 // pt = pt + 2
+	//ADD X1, X1, X0 // x1 = x0 // figure out where to put this
+	BL FindTail
+	//LDUR X0, [SP, #16] // reload X0
+
+rettail:
+	ADD X1, XZR, X0
+	LDUR FP, [SP, #0]
+	LDUR LR, [SP, #8]
+	ADDI SP, SP, #64
+	BR LR	
+
+FindMidpoint:
+	// input:
+	// x0: address of (pointer to) the first symbol of the symbol array
+	// x1: address of (pointer to) the last symbol of the symbol array
+	// x2: sum of the frequency of the left sub-array
+	// x3: sum of the frequency of the right sub-array
+
+	// output:
+	// x4: address of (pointer to) the first element of the right-hand side sub-array
+
+
+	SUBI	SP, SP, #64	// Allocate 32 bytes of memory (4 double words) to this function
+	STUR	FP, [SP, #0]	// FP of parent is saved onto my stack SP+0
+	STUR	LR, [SP, #8]	// LR should be saved to retrieve it later
+	ADDI	FP, SP, #56	// FP is moved up from parent's to mine
+
+if_mid:	ADD X4, XZR, X1 // stores tail in return register
+	ADDI X9, X0, #16 // checks if head + 2 == tail and returns tail if yes
+	SUBS XZR, X9, X4 // using X9 for temp storage
+	B.EQ retmid
+else_mid:
+	STUR X0, [SP, #16]	// First, make sure we backup registers that we need and are our
+	STUR X1, [SP, #24]
+	STUR X2, [SP, #32]
+	STUR X3, [SP, #40]
+	//STUR X4, [SP, #48]
+	SUBS XZR, X2, X3 // checks left_sum <= right_sum
+	B.LE if2_mid
+	// nested else statement
+else2_mid:	
+	SUBI X1, X1, #16 //tail = tail - 2
+	LDUR X10, [X1, #8] // *(tail + 1)
+	ADD X3, X3, X10 //right_sum = right_sum + *(tail + 1)
+	B endif_mid
+// nested if statement
+if2_mid:
+
+	ADDI X0, X0, #16 // head = head + 2
+	LDUR X10, [X0, #8] // X10 has *(head + 1)
+	ADD X2, X2, X10 // left_sum = left_sum + *(head + 1)
+endif_mid:
+	BL FindMidpoint // call FindMidpoint recursively
+	LDUR X0, [SP, #16]	// Restore the value of registers that we backed up
+	LDUR X1, [SP, #24]
+	LDUR X2, [SP, #32]
+	LDUR X3, [SP, #40]
+	//LDUR X4, [SP, #48]
+retmid:
+	LDUR	FP, [SP, #0]	// Restore FP to what it was at the start
+	LDUR	LR, [SP, #8]	// Restore LR to what it was at the start
+	ADDI	SP, SP, #64	// Free up the space we took on stack by moving SP	
+	br lr
+
+
+
+
+
+Partition:
+	// input:
+	// x0: address of (pointer to) the first symbol of the symbol array
+	// x1: address of (pointer to) the last symbol of the symbol array
+	// x2: address of the first attribute of the current binary tree node
+
+	SUBI	SP, SP, #64	// Allocate 64 bytes of memory (4 double words) to this function
+	STUR	FP, [SP, #0]	// FP of parent is saved onto my stack SP+0
+	STUR	LR, [SP, #8]	// LR should be saved to retrieve it later
+	ADDI	FP, SP, #56	// FP is moved up from parent's to mine
+
+
+	STUR X0, [X2, #0] //*node = start
+	STUR X1, [X2, #8] //*(node+1) = end
+if_part:
+	SUBS XZR, X0, X1 // checks if start = end
+	B.NE else_part
+	SUBI X9, XZR, #1 // storing NULL in X9
+	STUR X9, [X2, #16] // *(node + 2) = NULL
+	STUR X9, [X2, #24] // *(node + 3) = NULL
+	B retpart
+
+else_part:
+	STUR X0, [SP, #16]	// First, make sure we backup registers that we need and are our
+	STUR X1, [SP, #24]
+	STUR X2, [SP, #32]
+
+
+	LDUR X2, [X0, #8] // left_sum = *(start + 1)
+	LDUR X3, [X1, #8] // right_sum = *(end + 1)
+
+	BL FindMidpoint
+	LDUR X0, [SP, #16]	// Restore the value of registers that we backed up
+	LDUR X1, [SP, #24]
+	LDUR X2, [SP, #32]
+
+	ADD X10, X4, XZR // storing midpoint in X10
+	SUB X11, X10, X0 // offset = midpoint - start
+	SUBI X11, X11, #1 // offset = midpoint - start - 1
+	ADDI X12, X2, #32 // left_node = node + 4
+	LSL X11, X11, #2 // offset * 4
+	ADD X13, X12, X11 // right_node = node + 4 + offset * 4
+	STUR X12, [X2, #16] // *(node+2) = left_node
+	STUR X13, [X2, #24] // *(node+3) = right_node
+
+	SUBI X1, X10, #2 // end = midpoint - 2 before partition call
+	ADD X2, X12, XZR // node = left_node before partition call
+	BL Partition
+	LDUR X0, [SP, #16]	// Restore the value of registers that we backed up
+	LDUR X1, [SP, #24]
+	LDUR X2, [SP, #32]
+
+
+	ADD X0, X10, XZR // start = midpoint before partition call
+	ADD X2, X13, XZR // node = right_node before partition call
+	BL Partition
+	LDUR X0, [SP, #16]	// Restore the value of registers that we backed up
+	LDUR X1, [SP, #24]
+	LDUR X2, [SP, #32]
+
+
+retpart:
+	LDUR	FP, [SP, #0]	// Restore FP to what it was at the start
+	LDUR	LR, [SP, #8]	// Restore LR to what it was at the start
+	ADDI	SP, SP, #64	// Free up the space we took on stack by moving SP
+
+	br lr