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  17 <H3><A NAME="SEC24" HREF="suif1_toc.html#TOC24">Opcodes and Formats</A></H3>
  18 <P>
  19 <A NAME="IDX135"></A>
  20 <A NAME="IDX136"></A>
  21
  22 </P>
  23 <P>
  24 <A NAME="IDX137"></A>
  25 <A NAME="IDX138"></A>
  26 <A NAME="IDX139"></A>
  27 <A NAME="IDX140"></A>
  28 The <CODE>opcode</CODE> and <CODE>set_opcode</CODE> methods may be used to access
  29 the opcode field in an instruction.  These opcodes are members of the
  30 <CODE>if_ops</CODE> enumerated type.  The internal names for the opcodes all
  31 begin with <CODE>io_</CODE>, but that prefix is omitted in this documentation.
  32 The <CODE>if_ops_name</CODE> function takes an opcode and returns a character
  33 string holding the opcode name (without the <CODE>io_</CODE> prefix).  This is
  34 used by the library when it prints out instructions, but you may also
  35 call it directly.
  36
  37 </P>
  38 <P>
  39 <A NAME="IDX141"></A>
  40 <A NAME="IDX142"></A>
  41 <A NAME="IDX143"></A>
  42 Each opcode is associated with a particular instruction format.  The
  43 formats are specified by members of the <CODE>inst_format</CODE> enumeration.
  44 The <CODE>format</CODE> method may be used to retrieve the format for a
  45 particular instruction.  Alternatively, the <CODE>which_format</CODE> function
  46 takes an opcode and returns its format without reference to any
  47 particular instruction.  Each format corresponds to a particular derived
  48 instruction class:
  49
  50 </P>
  51 <DL COMPACT>
  52
  53 <DT><CODE>inf_rrr</CODE>
  54 <DD>
  55 Three operand instructions use the <CODE>in_rrr</CODE> class.
  56
  57 <DT><CODE>inf_bj</CODE>
  58 <DD>
  59 Branch and jump instructions use the <CODE>in_bj</CODE> class.
  60
  61 <DT><CODE>inf_ldc</CODE>
  62 <DD>
  63 The load constant instruction uses the <CODE>in_ldc</CODE> class.
  64
  65 <DT><CODE>inf_cal</CODE>
  66 <DD>
  67 The call instruction uses the <CODE>in_cal</CODE> class.
  68
  69 <DT><CODE>inf_array</CODE>
  70 <DD>
  71 The array instruction uses the <CODE>in_array</CODE> class.
  72
  73 <DT><CODE>inf_mbr</CODE>
  74 <DD>
  75 The multi-way branch instruction uses the <CODE>in_mbr</CODE> class.
  76
  77 <DT><CODE>inf_lab</CODE>
  78 <DD>
  79 The label instruction uses the <CODE>in_lab</CODE> class.
  80
  81 <DT><CODE>inf_gen</CODE>
  82 <DD>
  83 Generic instructions use the <CODE>in_gen</CODE> class.
  84 </DL>
  85
  86 <P>
  87 The <CODE>format</CODE> method is often used in <CODE>switch</CODE> statements for
  88 dealing with different kinds of instructions.  For example, the
  89 following code computes the number of source operands in an instruction
  90 (instead of using the <CODE>num_srcs</CODE> method):
  91
  92 </P>
  93
  94 <PRE>
  95 instruction *i;
  96 switch (i-&#62;format()) {
  97     case inf_rrr: {
  98         n += 2;
  99         break;
 100     }
 101     case inf_bj: {
 102         n += 1;
 103         break;
 104     }
 105     case inf_cal: {
 106         in_cal *cali = (in_cal *)i;
 107         n += 1 + cali-&#62;num_args();
 108         break;
 109     }
 110     case inf_array: {
 111         in_array *arri = (in_array *)i;
 112         n += 2 + 2 * arri-&#62;dims();
 113         break;
 114     }
 115     case inf_mbr: {
 116         n += 1;
 117         break;
 118     }
 119     case inf_gen: {
 120         in_gen *geni = (in_gen *)i;
 121         n += geni-&#62;num_srcs();
 122         break;
 123     }
 124     default: {
 125         /* other formats (inf_ldc and inf_lab) have no source operands */
 126         break;
 127     }
 128 }
 129 </PRE>
 130
 131 <P>
 132 The opcodes and instruction formats are defined in the <TT>`opcodes.h'</TT>
 133 and <TT>`opcodes.cc'</TT> files.
 134
 135 </P>
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