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Convert to an int16 (on the stack as int32) and throw an exception on overflow. Base instruction 0x83 conv.ovf.i2.un: Convert unsigned to an int16 (on the stack as int32) and throw an exception on overflow. Base instruction 0xB7 conv.ovf.i4: Convert to an int32 (on the stack as int32) and throw an exception on overflow. Base instruction 0x84
For example, INT 13H will generate the 20th software interrupt (0x13 is nineteen (19) in hexadecimal notation, and the count starts at 0), causing the function pointed to by the 20th vector in the interrupt table to be executed. INT is widely used in real mode. In protected mode, INT is a privileged instruction. [1]
New opcodes that introduced new functionality (e.g. SHLD, SETcc) For instruction forms where the operand size can be inferred from the instruction's arguments (e.g. ADD EAX,EBX can be inferred to have a 32-bit OperandSize due to its use of EAX as an argument), new instruction mnemonics are not needed and not provided.
In computing, an opcode (abbreviated from operation code) [1] [2] is an enumerated value that specifies the operation to be performed. Opcodes are employed in hardware devices such as arithmetic logic units (ALUs) and central processing units (CPUs) as well as in some software instruction sets.
Minimal instruction set computer (MISC) is a central processing unit (CPU) architecture, usually in the form of a microprocessor, with a very small number of basic operations and corresponding opcodes, together forming an instruction set. Such sets are commonly stack-based rather than register-based to reduce the size of operand specifiers.
An opcode table (also called an opcode matrix) is a visual representation of all opcodes in an instruction set. It is arranged such that each axis of the table represents an upper or lower nibble, which combined form the full byte of the opcode. Additional opcode tables can exist for additional instructions created using an opcode prefix.
When bit 15 of the opcode is set, it indicates that the 8-bit operand address in opcode bits 0–6 and 14 is extended to 16 bits using bits 0–7 of the following instruction word. Such instructions are written with an L prefix (LADD vs. ADD) and take an extra cycle to execute.
For example, the x86 architecture has available the 0x90 opcode; it is represented as NOP in the assembly source code. While it is possible to write programs directly in machine code, managing individual bits and calculating numerical addresses is tedious and error-prone.