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revision 1178, Mon Mar 25 20:51:48 2002 UTC revision 1181, Wed Mar 27 21:27:27 2002 UTC
# Line 14  Line 14 
14    
15  ----------------------------------------------------------------------  ----------------------------------------------------------------------
16  Name: Matthias Blume  Name: Matthias Blume
17    Date: 2002/03/27 16:27:00 EST
18    Tag: blume-20020327-mlrisc-divisions
19    Description:
20    
21    Added support for all four division operations (ML's div, mod, quot,
22    and rem) to MLRISC.  In the course of doing so, I also rationalized
23    the naming (no more annoying switch-around of DIV and QUOT), by
24    parameterizing the operation by div_rounding_mode (which can be either
25    DIV_TO_ZERO or DIV_TO_NEGINF).
26    
27    The generic MLTreeGen functor takes care of compiling all four
28    operations down to only round-to-zero div.
29    
30    Missing pieces:
31    
32      * Doing something smarter than relying on MLTreeGen on architectures
33        like, e.g., the x86 where hardware division delivers both quotient and
34        remainder at the same time.  With this, the implementation of the
35        round-to-neginf operations could be further streamlined.
36    
37      * Remove inlining support for div/mod/rem from the frontend and replace it
38        with primops that get carried through to the backend.  Do this for all
39        int and word types.
40    
41    ----------------------------------------------------------------------
42    Name: Matthias Blume
43    Date: 2002/03/25 17:25:00 EST
44    Tag: blume-20020325-divmod
45    Description:
46    
47    I improved (hopefully without breaking them) the implementation of Int.div,
48    Int.mod, and Int.rem.   For this, the code in translate.sml now takes
49    advantage of the following observations:
50    
51      Let  q = x quot y      r = x rem y
52           d = x div  y      m = x mod y
53    
54    where "quot" is the round-to-zero version of integer division that
55    hardware usually provides.  Then we have:
56    
57         r = x - q * y        where neither the * nor the - will overflow
58         d = if q >= 0 orelse x = q * y then q else q - 1
59                              where neither the * nor the - will overflow
60         m = if q >= 0 orelse r = 0 then r else r + y
61                              where the + will not overflow
62    
63    This results in substantial simplification of the generated code.
64    The following table shows the number of CFG nodes and edges generated
65    for
66            fun f (x, y) = x OPER y
67            (* with OPER \in div, mod, quot, rem *)
68    
69    
70        OPER | nodes(old) | edges(old) | nodes(new) | edges(new)
71        --------------------------------------------------------
72         div |         24 |         39 |         12 |         16
73         mod |         41 |         71 |         12 |         16
74        quot |          8 |         10 |          8 |         10
75         rem |         10 |         14 |          8 |         10
76    
77    
78    ----------------------------------------------------------------------
79    Name: Matthias Blume
80    Date: 2002/03/25 22:06:00 EST
81    Tag: blume-20020325-cprotobug
82    Description:
83    
84    Fixed a bug in cproto (c prototype decoder).
85    
86    ----------------------------------------------------------------------
87    Name: Matthias Blume
88  Date: 2002/03/25 16:00:00 EST  Date: 2002/03/25 16:00:00 EST
89  Tag: blume-20020325-raw-primops  Tag: blume-20020325-raw-primops
90  Description:  Description:

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