4.3. Bit Encoding for Itanium Instructions

Numerous type A Itanium instructions can share the same major opcode. They are differentiated from one another by a 2-bit opcode extension field in bits <35:34>. Most also have a second 2-bit opcode extension field in bits <28:27>, a 4-bit opcode extension field in bits <32:29>, and a 1-bit reserved opcode extension field in bit <33>.

Table 4-2 illustrates the bit encodings for the Itanium addition and subtraction instructions; nobody need actually memorize binary values for the machine instructions of any modern architecture. Compilers and assemblers convert human-readable mnemonic alphanumeric opcodes into binary machine instructions. Symbolic debuggers interpret binary machine instructions back into ...

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