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the loop loope loop while equal loopz loop while zero

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Unformatted text preview: n turn causes the handler routine for the interrupt or exception to be called. 7-24 Vol. 1 PROGRAMMING WITH GENERAL-PURPOSE INSTRUCTIONS The INT n instruction can raise any of the processor's interrupts or exceptions by encoding the vector number or the interrupt or exception in the instruction. This instruction can be used to support software generated interrupts or to test the operation of interrupt and exception handlers. The IRET (return from interrupt) instruction returns program control from an interrupt handler to the interrupted procedure. The IRET instruction performs a similar operation to the RET instruction. The CALL (call procedure) and RET (return from procedure) instructions allow a jump from one procedure to another and a subsequent return to the calling procedure. EFLAGS register contents are automatically stored on the stack along with the return instruction pointer when the processor services an interrupt. The INTO instruction raises the overflow exception if the OF flag is set. If the flag is clear, execution continues without raising the exception. This instruction allows software to access the overflow exception handler explicitly to check for overflow conditions. The BOUND instruction compares a signed value against upper and lower bounds, and raises the "BOUND range exceeded" exception if the value is less than the lower bound or greater than the upper bound. This instruction is useful for operations such as checking an array index to make sure it falls within the range defined for the array. Software Interrupt Instructions in 64-bit Mode and Compatibility Mode In 64-bit mode, the stack size is 8 bytes wide. IRET must pop 8-byte items off the stack. SS:RSP pops unconditionally. BOUND is not supported. In compatibility mode, SS:RSP is popped only if the CPL changes. 7.3.9 String Operations The MOVS (Move String), CMPS (Compare string), SCAS (Scan string), LODS (Load string), and STOS (Store string) instructions permit large data structures, such as alphanumeric character strings, to be moved and examined in memory. These instructions operate on individual elements in a string, which can be a byte, word, or doubleword. The string elements to be operated on are identified with the ESI (source string element) and EDI (destination string element) registers. Both of these registers contain absolute addresses (offsets into a segment) that point to a string element. By default, the ESI register addresses the segment identified with the DS segment register. A segment-override prefix allows the ESI register to be associated with the CS, SS, ES, FS, or GS segment register. The EDI register addresses the segment identified with the ES segment register; no segment override is allowed for the EDI register. The use of two different segment registers in the string instructions permits operations to be performed on strings located in different segments. Or by associ- Vol. 1 7-25 PROGRAMMING WITH GENERAL-PURPOSE INSTRUCTION...
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