Code:
###DATA SECTION###
.data
##GLOBAL VARIABLE##
#Alignment is _critical_ in SPU applications.
#This aligns to a 16-byte (128-bit) boundary
.align 4
#This is the number
number:
.long 18
.align 4
output:
.ascii "The factorial of %d is %d\n\0"
##STACK OFFSETS##
#Offset in the stack frame of the link register
.equ LR_OFFSET, 16
#Size of main's stack frame (back pointer + return address)
.equ MAIN_FRAME_SIZE, 32
#Size of factorial's stack frame (back pointer + return address + local variable)
.equ FACT_FRAME_SIZE, 48
#Offset in the factorial's stack frame of the local "num" variable
.equ LCL_NUM_VALUE, 32
###CODE SECTION###
.text
##MAIN ENTRY POINT
.global main
.type main,@function
main:
#PROLOGUE#
stqd $lr, LR_OFFSET($sp)
stqd $sp, -MAIN_FRAME_SIZE($sp)
ai $sp, $sp, -MAIN_FRAME_SIZE
#FUNCTION BODY#
#Load number as the first parameter (relative addressing)
lqr $3, number
#Call factorial
brsl $lr, factorial
#Display Factorial
#Result is in register 3 - move it to register 5 (third parameter)
lr $5, $3
#Load output string into register 3 (first parameter)
ila $3, output
#Put original number in register 4 (second parameter)
lqr $4, number
#Call printf (this actually runs on the PPE)
brsl $lr, printf
#Load register 3 with a return value of 0
il $3, 0
#EPILOGUE#
ai $sp, $sp, MAIN_FRAME_SIZE
lqd $lr, LR_OFFSET($sp)
bi $lr
##FACTORIAL FUNCTION
factorial:
#PROLOGUE#
#Before we set up our stack frame,
#store link register in caller's frame
stqd $lr, LR_OFFSET($sp)
#Store back pointer before reserving the stack space
stqd $sp, -FACT_FRAME_SIZE($sp)
#Move stack pointer to reserve stack space
ai $sp, $sp, -FACT_FRAME_SIZE
#END PROLOGUE#
#Save arg 1 in local variable space
stqd $3, LCL_NUM_VALUE($sp)
#Compare to 0, and store comparison in reg 4
ceqi $4, $3, 0
#Do we jump? (note that the "zero" we are comparing
#to is the result of the above comparison)
brnz $4, case_zero
case_not_zero:
#remove 1, and use it as the function argument
ai $3, $3, -1
#call factorial function (return value in reg 3)
brsl $lr, factorial
#Load in the value of the current number
lqd $5, LCL_NUM_VALUE($sp)
#multiply the last factorial answer with the current number
#store the answer in register 3 (the return value register)
mpyu $3, $3, $5
#EPILOGUE#
#Restore previous stack frame
ai $sp, $sp, FACT_FRAME_SIZE
#Restore link register
lqd $lr, LR_OFFSET($sp)
#Return
bi $lr
case_zero:
#Put 1 in reg 3 for the return value
il $3, 1
##EPILOGUE##
#Restore previous stack frame
ai $sp, $sp, FACT_FRAME_SIZE
#Return
bi $lr Props to 
Originally Posted by xxkrizxx 
