ARM64 fibo asm

fibo.asm

.section __DATA,__data
	phi_const:
		.double 1.618033988749895
	root5_const:
		.double 2.23606797749979
	msg:
		.asciz "Hello, ARM64 macOS!\n"

.section __TEXT,__text
    .global _hello
    .global _main
    .global fibo
    .p2align 3 // 8-byte alignment 2 ^ 3

    .macro FUNC_PROLOGUE
        stp x29, x30, [sp, #-16]!
        mov x29, sp
    .endm

    .macro FUNC_EPILOGUE
        ldp x29, x30, [sp], #16
        ret
    .endm

_hello:
    FUNC_PROLOGUE
    // sys_write: write(1, msg, len)
    mov x0, 1            // file descriptor (stdout)
    adrp x1, msg@PAGE    // load page address of msg
    add x1, x1, msg@PAGEOFF // load offset of msg
    mov x2, 20           // length of string
    mov x16, 0x4         // syscall number for write
    svc 0                // trigger syscall
    FUNC_EPILOGUE

_fibo:
    FUNC_PROLOGUE
    stp x19, x20, [sp, #-16]!   // Save x19, x20 (callee-saved)

    cmp x0, 1
    ble .FiboBaseReturn

    mov x19, x0        // Save n
    sub x0, x0, 1      // n-1
    bl _fibo           // fibo(n-1)
    mov x20, x0        // Save fibo(n-1)

    sub x0, x19, 2     // n-2
    bl _fibo           // fibo(n-2)

    add x0, x0, x20    // fibo(n-1) + fibo(n-2)

    b .FiboEndFunc

.FiboBaseReturn:
    // Base case: return x0 as is

.FiboEndFunc:
    ldp x19, x20, [sp], #16     // Restore x19, x20
    FUNC_EPILOGUE

_fibo_iterative:
    FUNC_PROLOGUE
    stp x19, x20, [sp, #-16]!    // Save callee-saved

    cmp x0, 1
    ble .FiboEnd                 // If n <= 1, return n as is

    mov x19, 0                   // a = 0
    mov x20, 1                   // b = 1
    mov x21, 2                   // i = 2

.Loop:
    cmp x21, x0                  // while (i <= n)
    bgt .FiboEnd

    add x22, x19, x20            // temp = a + b
    mov x19, x20                 // a = b
    mov x20, x22                 // b = temp

    add x21, x21, 1              // i++
    b .Loop

.FiboEnd:
    mov x0, x20                  // return b

    ldp x19, x20, [sp], #16
    FUNC_EPILOGUE
	
_fibo_fast:
    FUNC_PROLOGUE
    stp d8, d9, [sp, #-16]!        // Save callee-saved FP registers

    // Load constants phi and sqrt(5)
    adrp x1, phi_const@PAGE
    ldr d8, [x1, phi_const@PAGEOFF]

    adrp x1, root5_const@PAGE
    ldr d9, [x1, root5_const@PAGEOFF]

    // Prepare pow arguments: base=phi in d0, exponent=n in d1 (double)
    fmov d0, d8                   // d0 = phi (base)
    scvtf d1, x0                 // d1 = double(n) (exponent)
    bl _pow                      // call pow(base, exponent)

    // Divide result by sqrt(5)
    fdiv d0, d0, d9

    // Round to nearest integer
    frintn d0, d0

    // Convert double to int64
    fcvtzs x0, d0

    ldp d8, d9, [sp], #16        // Restore FP registers
    FUNC_EPILOGUE


_main:
    FUNC_PROLOGUE            

    bl _hello     

    mov x0, 277// calculate fibo sum upto 5 numbers
    bl _fibo_fast

    ldp x29, x30, [sp], #16

    mov x16, 1 // exit syscall