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Chapter 21. 80386 Dependent Features

multiply; the expanding multiply would clobber the

%edx

register, and this would confuse

gcc

output.

Use

imul %ebx

to get the 64 bit product in

%edx:%eax

.

We have added a two operand form of

imul

when the first operand is an immediate mode expression

and the second operand is a register. This is just a shorthand, so that, multiplying

%eax

by 69, for

example, can be done with

imul $69, %eax

rather than

imul $69, %eax, %eax

.