Added description. x86 solutions for some problemsHEADmaster

5 files changed, 89 insertions, 0 deletions

diff --git a/04-Largest-Palindrome-Product/asm/Makefile b/04-Largest-Palindrome-Product/asm/Makefile
new file mode 100644
index 0000000..53b33b2
--- /dev/null
+++ b/04-Largest-Palindrome-Product/asm/Makefile
@@ -0,0 +1,6 @@
+palindrome: palindrome.o
+	gcc palindrome.o -o palindrome 
+palindrome.o: palindrome.asm
+	nasm -w+all -f elf64 -g -F stabs palindrome.asm
+clean:
+	rm -f palindrome palindrome.o
diff --git a/04-Largest-Palindrome-Product/asm/palindrome b/04-Largest-Palindrome-Product/asm/palindrome
new file mode 100755
index 0000000..3f75c67
--- /dev/null
+++ b/04-Largest-Palindrome-Product/asm/palindrome
diff --git a/04-Largest-Palindrome-Product/asm/palindrome.asm b/04-Largest-Palindrome-Product/asm/palindrome.asm
new file mode 100644
index 0000000..03cd724
--- /dev/null
+++ b/04-Largest-Palindrome-Product/asm/palindrome.asm
@@ -0,0 +1,83 @@
+; Find the largest palindrome made from the product of two 3-digit numbers.
+
+extern printf
+SECTION .data
+flag:   db  "%d",10,0           ; "%d\n\0"
+
+SECTION .text
+    global main    
+    global is_palindrome
+
+is_palindrome:
+; check if the product in rax is a palindrome
+        
+        push rax                ; save the value
+        xor r14, r14            ; using this as a string length counter
+.div:   xor rdx, rdx            ; clear operand for div
+        div r12                 ; rdx:rax / 10
+        add rdx, 0x30           ; digit is in remainder, add ascii 0
+        push rdx
+        inc r14
+        cmp rax, 0
+        jnz .div
+        
+; Cheating a bit here. Highest product of two 3 digit numbers will
+; not exceed 6 digits. We assume only three comparisons need to made
+; 5 digit numbers are excluded outright
+
+        cmp r14, 6
+        jne main.nexti          ; return
+        mov rax, [rsp]
+        mov rdx, [rbp-0x18]     ; at this point, original rbp, ret and rax are
+        cmp rax, rdx            ; on the stack, so skip three qwords (64bits)
+        jne main.nexti
+        mov rax, [rsp+8]
+        mov rdx, [rbp-0x20]
+        cmp rax, rdx 
+        jne main.nexti
+        mov rax, [rsp+16]
+        mov rdx, [rbp-0x28]
+        cmp rax, rdx 
+        jne main.nexti
+        ; if you made it here, rax is a palindrome!
+        mov rsp, rbp            ; reset stack back to the first variable
+        sub rsp, 16             ; first 8 bytes is the return call
+        pop rax
+        ret
+
+main:
+        push rbp                ; set up stack
+        mov rbp, rsp
+        mov r11, 0x3E7          ; j=999
+        mov r12, 0xA            ; for division testing later
+        xor r13, r13            ; current max palindrome (0)
+; check products for three digit numbers (starting with highest)
+.loopj  mov rcx, 0x3E7          ; setup counter two (i=999)
+
+.loopi  xor rdx, rdx            ; clear operand for mul
+        mov rax, r11            ; operand for mul 
+        mul rcx                 ; rdx:rax = rax * rcx (j * i)
+                                ; hint this won't overflow
+        call is_palindrome
+        ; if you made it here, rax is a palindrome!
+        cmp rax, r13            ; if rax is not bigger than the current max
+        jl .nexti               ; next loop
+        mov r13, rax            ; otherwise, update value 
+
+.nexti: mov rsp, rbp            ; reset stack (if needed)
+        loopnz .loopi           ; i = 0, decrement j and restart
+        
+        dec r11                 ; j--
+        jnz .loopj
+
+.print  mov rdi, flag           ; arg 1 (format)
+        mov rsi, r13            ; arg 2
+        mov rax, 0		; no xmm registers
+        call printf wrt ..plt
+
+        mov rsp, rbp            ; reset to the top of the stack
+        pop rbp
+
+        mov rax, 0
+        ret
+
diff --git a/04-Largest-Palindrome-Product/asm/palindrome.o b/04-Largest-Palindrome-Product/asm/palindrome.o
new file mode 100644
index 0000000..6f1d9da
--- /dev/null
+++ b/04-Largest-Palindrome-Product/asm/palindrome.o
diff --git a/04-Largest-Palindrome-Product/palindrome b/04-Largest-Palindrome-Product/palindrome
index f4d607f..f4d607f 100644..100755
--- a/04-Largest-Palindrome-Product/palindrome
+++ b/04-Largest-Palindrome-Product/palindrome