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Unformatted text preview: aled Indexed Scaled Indexed Scaled Indexed ÁÑÑ () ÁÑÑ ( ) (,) ÁÑÑ ( , ) (, ,×) ÁÑÑ (, ,×) ( , , ×) ÁÑÑ ( , ,×) · Ê ¡×
Ê ¡× Figure 3.3: Operand Forms. Operands can denote immediate (constant) values, register values, or values from memory. The scaling factor × must be either 1, 2, 4, or 8. registers (%ebp and %esp) contain pointers to important places in the program stack. They should only be altered according to the set of standard conventions for stack management. As indicated in Figure 3.2, the low-order two bytes of the ﬁrst four registers can be independently read or written by the byte operation instructions. This feature was provided in the 8086 to allow backward compatibility to the 8008 and 8080—two 8-bit microprocessors that date back to 1974. When a byte instruction updates one of these single-byte “register elements,” the remaining three bytes of the register do not change. Similarly, the low-order 16 bits of each register can be read or written by...
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- Spring '10
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