39 lines
1.9 KiB
Markdown
39 lines
1.9 KiB
Markdown
---
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layout: page
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title: "x86 Instructions: AAD"
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permalink: /docs/x86/ops/AAD/
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---
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AAD (0xD5)
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---
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### Description
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From [http://www.rcollins.org/secrets/opcodes/AAD.html](http://www.rcollins.org/secrets/opcodes/AAD.html):
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Undocumented: Available to all Intel x86 processors
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Useful in production source code.
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AAD
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Flags: ASCII Adjust before Division
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+-+-+-+-+-+-+-+-+-+ +----------+----------+
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|O|D|I|T|S|Z|A|P|C| | 11010101 | DATA |
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+-+-+-+-+-+-+-+-+-+ +----------+----------+
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|+| | | |+|+|+|+|+| | D5 | IMM8 |
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+-+-+-+-+-+-+-+-+-+ +----------+----------+
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This instruction is the multiplication counterpart to AAM. As is the case with AAM, AAD uses the second byte
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as an operand. This operand is the multiplicand for AAD. Like AAM, AAD provides a way to execute a MUL IMM8 that
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is unavailable through any other means in the CPU. Unlike MUL, or IMUL, AAD sets all of the CPU status flags
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according to the result. Intel states that the Overflow Flag (OF), Auxiliary carry Flag (AF), and Carry Flag (CF)
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are undefined. This assertion is incorrect. These flags are fully defined, and are set consistently with respect
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to any other integer operations. And again, like AMM, beginning with the Pentium, Intel has finally acknowledged
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the existence of the second byte of this instruction as its operand. Intel says:
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Note: imm8 has the value of the instruction's second byte. The second byte under normally assembly [sic] of
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this instruction will be 0A, however, explicit modification of this byte will result in the operation described
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above and may alter results.
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This instruction exists in this form on all Intel x86 processors. See the file AAD.ASM for diagnostics source code
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for this instruction.
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See [AAD.ASM](AAD.ASM) for the source code mentioned above.
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