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Factorial of a number

The following assembly program calculates the factorial of a number. The number to calculate factorial is stored in a memory location (_data1 + 4). The result is stored in memory location (_data1+8). The '_data1' is a label.

Before starting, please ensure spiking folder is downloaded .

cd spiking

Open a file in a text editor and save it inside spiking folder

vim factorial.S

gedit factorial.S

factorial.S content:

      la    x5, _data1   	# setting sp to point to 0x10011000
      lwu   sp, 0(x5)
      mv    a0,x0	   	# initializing 4 registers to zero.
      mv    a5,x0
      mv    a4,x0
      mv    a7,x0
      lw    a0,4(x5)     	# the number whose factorial to be calculated is stored in data1, which is loaded here
      jal   ra,_fact
      mv    a7,a0        	# Final Value stored in a7
      sw    a7,8(x5)
      ebreak
      j     _start
_fact:
      addi  sp,sp,-32    	# sp= sp-32
      sd    ra,24(sp)    	# STORE return Address,    Memory[24+sp]=ra
      sd    s0,16(sp)    	# STORE s0, Memory[16+sp]=s0
      addi  s0,sp,32     	# s0=sp+32 Frame pointer
      mv    a5,a0        	# a5=a0
      sw    a5,-20(s0)   	# STORE a5 in stack, Memory[s0-20]=a5
      beqz  a5, J1 	   	# Branch to address 10010032 if (a5==0)
      addiw a5,a5,-1     	# a5=a5-1
      mv    a0,a5        	# a5=a0
      jal   ra,_fact     	# jump and ra = PC+4
      mv    a4,a0        	# a4=a5
      lw    a5,-20(s0)   	# a5 = Memory [s0-20]
      mul   a5,a5,a4     	# a5=a5+a4
      mv    a0,a5        	# a0 =a5
      ld    ra,24(sp)    	# ra = Memory[sp+24]
      ld    s0,16(sp)    	# s0 = Memory[sp+16]
      addi  sp,sp,32     	# sp=sp+32
      ret                	# return to main function
J1:
      addi  a0,x0,1      	# a0=1
      ld    ra,24(sp)    	# ra = Memory[sp+24]
      ld    s0,16(sp)    	# s0 = Memory[sp+16]
      addi  sp,sp,32     	# sp=sp+32
      ret
  .section .data         	# data section starts
  .p2align 0x2           	# aligned to eight bytes
  _data1:
  .word 0x10011000       	# First data in data section
  .word 0x2              	# X-Number whose factorial is calculated -F(X)

Compile

Before starting compilation, Please check if the shakti-tools are successfully installed.

Please ensure you're inside spiking folder and run the below command

riscv64-unknown-elf-gcc -nostdlib -nostartfiles -T spike.lds  factorial.S -o factorial.elf

On successful compilation, an executable binary named factorial.elf will be generated.

Execute

The asm program can be run using spike, or with RISC-V GDB or using Axtix-7 100t

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Factorial of a number

Open a file in a text editor and save it inside spiking folder

Compile

Execute

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