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   6 <TITLE>The SUIF Version 1 Library - Target Machine Parameters</TITLE>
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  17 <H2><A NAME="SEC103" HREF="suif1_toc.html#TOC103">Target Machine Parameters</A></H2>
  18 <P>
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  20
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  22 <P>
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  25 The SUIF library includes a structure to record various parameters of
  26 the target machine.  The back-end of the compiler may be either a code
  27 generator for a specific processor or the system's C compiler, using the
  28 SUIF-to-C translator.  Thus, the target machine parameters include
  29 fields that deal both with hardware requirements and with details of the
  30 back-end C compiler.  These parameters are stored in the <CODE>target</CODE>
  31 <CODE>machine_params</CODE> structure.  The front-end is responsible for
  32 setting the target parameters, but they are then saved in the SUIF files
  33 and passed along to all subsequent passes of the compiler.
  34
  35 </P>
  36 <P>
  37 The first fields in the <CODE>machine_params</CODE> structure deal with the
  38 addressing in the underlying hardware.  The <CODE>is_big_endian</CODE> field
  39 specifies the byte order, and the <CODE>addressable_size</CODE> field
  40 specifies the size in bits of the smallest addressable unit.  Since most
  41 machines are byte-addressable, the <CODE>addressable_size</CODE> is usually
  42 set to eight.
  43
  44 </P>
  45 <P>
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  47 Next, the sizes and alignments for various C types are specified.  The
  48 possible C types are listed in the <CODE>C_types</CODE> enumeration:
  49
  50 </P>
  51 <DL COMPACT>
  52
  53 <DT><CODE>C_char</CODE>
  54 <DD>
  55 <DT><CODE>C_short</CODE>
  56 <DD>
  57 <DT><CODE>C_int</CODE>
  58 <DD>
  59 <DT><CODE>C_long</CODE>
  60 <DD>
  61 <DT><CODE>C_longlong</CODE>
  62 <DD>
  63 <DT><CODE>C_float</CODE>
  64 <DD>
  65 <DT><CODE>C_double</CODE>
  66 <DD>
  67 <DT><CODE>C_longdouble</CODE>
  68 <DD>
  69 <DT><CODE>C_ptr</CODE>
  70 <DD>
  71 </DL>
  72
  73 <P>
  74 The <CODE>size</CODE> and <CODE>align</CODE> fields of the <CODE>machine_params</CODE>
  75 structure are arrays containing the size and alignment for each C type.
  76 Both are specified in bits (not bytes).  Some C compilers require
  77 additional alignment restrictions for arrays and structures.  The
  78 <CODE>array_align</CODE> and <CODE>struct_align</CODE> fields contain these
  79 alignment requirements in bits.  Note that these do not replace the
  80 alignment restrictions for the components of an array or structure; the
  81 most restrictive alignments must always be maintained.
  82
  83 </P>
  84 <P>
  85 The remaining fields are only applicable to the back-end C compiler.
  86 The <CODE>char_is_signed</CODE> field specifies if the default <CODE>char</CODE>
  87 type is signed.  This is just to allow the SUIF-to-C translator to avoid
  88 cluttering up the C code by explicitly putting <CODE>signed</CODE> or
  89 <CODE>unsigned</CODE> in every declaration of a <CODE>char</CODE> type.  When two
  90 pointers are subtracted in C, the result type is implementation defined.
  91 The <CODE>ptr_diff_type</CODE> field in <CODE>machine_params</CODE> specifies the
  92 type produced by such pointer subtractions for use in SUIF-to-C.
  93
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