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Unformatted text preview: word operation instructions. This feature stems from IA32’s evolutionary heritage as a 16-bit microprocessor. 3.4.1 Operand Speciﬁers
Most instructions have one or more operands, specifying the source values to reference in performing an operation and the destination location into which to place the result. IA32 supports a number of operand forms (Figure 3.3). Source values can be given as constants or read from registers or memory. Results can be stored in either registers or memory. Thus, the different operand possibilities can be classiﬁed into three types. The ﬁrst type, immediate, is for constant values. With GAS, these are written with a ‘$’ followed by an integer using standard C notation, such as, $-577 or $0x1F. Any value that ﬁts in a 32-bit word can be used, although the assembler will use one or two-byte encodings when possible. The second type, register, denotes the contents of one of the registers, either one of the eight 32-bit registers (e.g., %eax) for a double-word operat...
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