1 files changed, 86 insertions, 0 deletions
diff --git a/PGU/CHAP10/int2str.s b/PGU/CHAP10/int2str.s
new file mode 100644
index 0000000..6ea5178
--- /dev/null
+++ b/PGU/CHAP10/int2str.s
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+# integer2string
+#
+# Convert an int number to a decima string for display
+#
+# Receives a buffer large enough to hold the largest possible numberr
+# and an integer to convert
+#
+# %rcx hold the count of characters processed
+# %rax holds the current value
+# %rdi hold the base (10)
+
+.equ ST_VALUE, 16
+.equ ST_BUFFER, 24
+
+.globl integer2string
+.type integer2string, @function
+
+integer2string:
+
+	# Default function setup
+	pushq %rbp
+	movq %rsp, %rbp
+
+	movq $0, %rcx	# Init char count
+	movq ST_VALUE(%rbp), %rax	# Retrieve value from stack
+
+	# The divisor must be in a register or memory location
+	movq $10, %rdi
+
+	conversion_loop:
+		# Division is actually performed on the combined
+		# %rdx:%rax register, so first, clear out %rdx
+		movq $0, %rdx
+
+		# Divide %rdx:%rax (which are implied) by 10
+		# Store the quotient in %rax and the remainder in
+		# %rdx (both which are implied)
+		divq %rdi
+
+		# Quotient is in the right place. %rdx has the remainder
+		# which now needs to be converted into a number. So, %rdx has a
+		# number that is 0 through 9. We'll use it as an 'index' on the
+		# ASCII table starting from char '0'.
+		addq $'0', %rdx	# Get our number's index from ASCII
+					# table, starting from '0'.
+
+		# Push this value into the stack. When we are done, we can just
+		# pop them off one-by-one, and they will be in the right order.
+		# NOTE: We are pushing the whole register, but we only need the
+		# byte in %dl (The last byte of the %rdx register) for the
+		# character.
+		pushq %rdx
+
+		incq %rcx	# Increment digit count
+
+		cmpq $0, %rax	# Have we reached the end of the calculation?
+		je end_conversion_loop
+
+		# %rax has its new value
+		jmp conversion_loop
+
+	end_conversion_loop:
+		# The string is now on the stack, if we pop it off a char at a
+		# time, we can copy it into the buffer and we are done.
+
+		movq ST_BUFFER(%rbp), %rdx	# Move buffer address to %rdx
+
+	copy_reversing_loop:
+		popq %rax
+		movb %al, (%rdx)
+		decq %rcx	# Once we reach 0 we are finished
+		incq %rdx	# Point to the next byte
+
+		cmpq $0, %rcx	# Check if we are finished
+		je end_copy_reversing_loop
+
+		jmp copy_reversing_loop
+
+	end_copy_reversing_loop:
+		movb $0, (%rdx)
+
+	movq %rbp, %rsp
+	popq %rbp
+	ret
+
+# end of integer2string