2.1. WORKING WITH INTEGERS |
35 |
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2.1.4 |
Example program |
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math.asm |
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1 |
%include "asm_io.inc" |
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2 |
segment .data |
; Output strings |
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3 |
prompt |
db |
"Enter a number: ", 0 |
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4 |
square_msg |
db |
"Square of input is ", 0 |
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5 |
cube_msg |
db |
"Cube of input is ", 0 |
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6 |
cube25_msg |
db |
"Cube of input times 25 is ", 0 |
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7 |
quot_msg |
db |
"Quotient of cube/100 is ", 0 |
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8 |
rem_msg |
db |
"Remainder of cube/100 is ", 0 |
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9 |
neg_msg |
db |
"The negation of the remainder is ", 0 |
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10 |
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11 |
segment .bss |
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12 |
input resd 1 |
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13
14segment .text
15global _asm_main
16_asm_main:
17 |
enter |
0,0 |
; setup routine |
18 |
pusha |
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19 |
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mov |
eax, prompt |
call |
print_string |
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call |
read_int |
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mov |
[input], eax |
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imul |
eax |
; edx:eax = eax * eax |
mov |
ebx, eax |
; save answer in ebx |
mov |
eax, square_msg |
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call |
print_string |
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mov |
eax, ebx |
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call |
print_int |
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call |
print_nl |
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mov |
ebx, eax |
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imul |
ebx, [input] |
; ebx *= [input] |
mov |
eax, cube_msg |
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call |
print_string |
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mov |
eax, ebx |
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call |
print_int |
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call |
print_nl |
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36 |
CHAPTER 2. BASIC ASSEMBLY LANGUAGE |
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imul |
ecx, ebx, 25 |
; ecx = ebx*25 |
mov |
eax, cube25_msg |
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call |
print_string |
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mov |
eax, ecx |
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call |
print_int |
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call |
print_nl |
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mov |
eax, ebx |
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cdq |
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; initialize edx by sign extension |
mov |
ecx, 100 |
; can’t divide by immediate value |
idiv |
ecx |
; edx:eax / ecx |
mov |
ecx, eax |
; save quotient into ecx |
mov |
eax, quot_msg |
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call |
print_string |
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mov |
eax, ecx |
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call |
print_int |
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call |
print_nl |
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mov |
eax, rem_msg |
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call |
print_string |
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mov |
eax, edx |
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call |
print_int |
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call |
print_nl |
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neg |
edx |
; negate the remainder |
mov |
eax, neg_msg |
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call |
print_string |
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mov |
eax, edx |
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call |
print_int |
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call |
print_nl |
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popa |
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mov |
eax, 0 |
; return back to C |
leave |
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ret |
math.asm |
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2.1.5Extended precision arithmetic
Assembly language also provides instructions that allow one to perform addition and subtraction of numbers larger than double words. These instructions use the carry flag. As stated above, both the ADD and SUB instructions modify the carry flag if a carry or borrow are generated, respectively.