How many lw
instructions will be needed?
One, near the start
of the program to load x into a register.
How many sw
instructions will be needed?
One, near the end
of the program to save the result in poly.
## poly.asm
##
## evaluate 5x^2 -12x + 97
##
.text
.globl main
main:
. . . . many instructions
.data
# In SPIM, the data section
# starts at address 0x10000000
x: .word 17 # The base register points here.
poly: .word 0
## End of file
In the description of this problem, memory locations
are called x and poly.
Of course, at run time, addresses are 32-bit patterns.
In assembly language source code, it is convenient to use names for memory locations. These names are called symbolic addresses.
One of the most important features of an assembler is support for symbolic addresses. In the following example we will ignore some of this support in favor of explaining how the hardware instructions work.
In the above (incomplete) sample program,
x is a symbolic address.
It corresponds to the address where, at run-time, four bytes hold a two's complement 17.
The assembler directive .data means:
here is the start of the data section of memory.
The assembler directive .word means:
put a 32-bit two's complement integer here.
The integer is specified using base 10 (by default).
In the above, the .word 17 calls for a 32-bit two's complement
representation of an integer that in base 10 is "17".
The assembler converts the representation into the appropriate bit pattern.
You can also specify the bit pattern using the hexadecimal name for the pattern.
.word 0x11 does exactly the same thing as .word 17.
The assembler in SPIM automatically assembles the .data section starting at address 0x10000000.
x?poly?