hw/i386.reference/AAS.htm

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   4 <TITLE>80386 Programmer's Reference Manual -- Opcode AAS</TITLE>
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   7 <B>up:</B> <A HREF="c17.htm">
   8 Chapter 17 -- 80386 Instruction Set</A><BR>
   9 <B>prev:</B><A HREF="AAM.htm"> AAM ASCII Adjust AX after Multiply</A><BR>
  10 <B>next:</B><A HREF="ADC.htm"> ADC Add with Carry</A>
  11 <P>
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  13 <P>
  14 <H1>AAS -- ASCII Adjust AL after Subtraction</H1>
  15
  16 <PRE>
  17 Opcode    Instruction    Clocks    Description
  18
  19 3F        AAS            4         ASCII adjust AL after subtraction
  20 </PRE>
  21
  22 <H2>Operation</H2>
  23
  24 <PRE>
  25 IF (AL AND 0FH) > 9 OR AF = 1
  26 THEN
  27    AL := AL - 6;
  28    AL := AL AND 0FH;
  29    AH := AH - 1;
  30    AF := 1;
  31    CF := 1;
  32 ELSE
  33    CF := 0;
  34    AF := 0;
  35 FI;
  36 </PRE>
  37
  38 <H2>Description</H2>
  39
  40 Execute AAS only after a
  41 <A HREF="SUB.htm">SUB</A> instruction that leaves the byte result in the
  42 AL register. The lower nibbles of the operands of the
  43 <A HREF="SUB.htm">SUB</A> instruction must
  44 have been in the range 0 through 9 (BCD digits). In this case, AAS adjusts
  45 AL so it contains the correct decimal digit result. If the subtraction
  46 produced a decimal carry, the AH register is decremented, and the carry and
  47 auxiliary carry flags are set to 1. If no decimal carry occurred, the carry
  48 and auxiliary carry flags are set to 0, and AH is unchanged. In either case,
  49 AL is left with its top nibble set to 0. To convert AL to an ASCII result,
  50 follow the AAS with <A HREF="OR.htm">OR</A> AL, 30H.
  51
  52 <H2>Flags Affected</H2>
  53
  54 AF and CF as described above; OF, SF, ZF, and PF are undefined
  55
  56 <H2>Protected Mode Exceptions</H2>
  57
  58 None
  59
  60 <H2>Real Address Mode Exceptions</H2>
  61
  62 None
  63
  64 <H2>Virtual 8086 Mode Exceptions</H2>
  65
  66 None
  67
  68
  69 <P>
  70 <HR>
  71 <P>
  72 <B>up:</B> <A HREF="c17.htm">
  73 Chapter 17 -- 80386 Instruction Set</A><BR>
  74 <B>prev:</B><A HREF="AAM.htm"> AAM ASCII Adjust AX after Multiply</A><BR>
  75 <B>next:</B><A HREF="ADC.htm"> ADC Add with Carry</A>
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