3463d993f1385e55511e0e140dd09576403c23ef
1 # IEEE Floating Point Adder (Single Precision)
2 # Copyright (C) Jonathan P Dawson 2013
5 from nmigen
import Module
, Signal
, Cat
, Const
6 from nmigen
.cli
import main
, verilog
9 from nmutil
.pipemodbase
import PipeModBase
, PipeModBaseChain
10 from ieee754
.fpcommon
.fpbase
import FPNumDecode
12 from ieee754
.fpcommon
.fpbase
import FPNumBaseRecord
13 from ieee754
.fpcommon
.basedata
import FPBaseData
14 from ieee754
.fpcommon
.denorm
import (FPSCData
, FPAddDeNormMod
)
17 class FPAddSpecialCasesMod(PipeModBase
):
18 """ special cases: NaNs, infs, zeros, denormalised
19 NOTE: some of these are unique to add. see "Special Operations"
20 https://steve.hollasch.net/cgindex/coding/ieeefloat.html
23 def __init__(self
, pspec
):
24 super().__init
__(pspec
, "specialcases")
27 return FPBaseData(self
.pspec
)
30 return FPSCData(self
.pspec
, True)
32 def elaborate(self
, platform
):
36 # decode: XXX really should move to separate stage
37 width
= self
.pspec
.width
38 a1
= FPNumBaseRecord(width
)
39 b1
= FPNumBaseRecord(width
)
40 m
.submodules
.sc_decode_a
= a1
= FPNumDecode(None, a1
)
41 m
.submodules
.sc_decode_b
= b1
= FPNumDecode(None, b1
)
42 comb
+= [a1
.v
.eq(self
.i
.a
),
48 # temporaries used below
49 s_nomatch
= Signal(reset_less
=True)
50 m_match
= Signal(reset_less
=True)
51 e_match
= Signal(reset_less
=True)
52 aeqmb
= Signal(reset_less
=True)
53 abz
= Signal(reset_less
=True)
54 absa
= Signal(reset_less
=True)
55 abnan
= Signal(reset_less
=True)
56 bexp128s
= Signal(reset_less
=True)
58 comb
+= s_nomatch
.eq(a1
.s
!= b1
.s
)
59 comb
+= m_match
.eq(a1
.m
== b1
.m
)
60 comb
+= e_match
.eq(a1
.e
== b1
.e
)
61 comb
+= aeqmb
.eq(s_nomatch
& m_match
& e_match
)
62 comb
+= abz
.eq(a1
.is_zero
& b1
.is_zero
)
63 comb
+= absa
.eq(a1
.s
& b1
.s
)
64 comb
+= abnan
.eq(a1
.is_nan | b1
.is_nan
)
65 comb
+= bexp128s
.eq(b1
.exp_128
& s_nomatch
)
67 # prepare inf/zero/nans
68 z_zero
= FPNumBaseRecord(width
, False, name
="z_zero")
69 z_nan
= FPNumBaseRecord(width
, False, name
="z_nan")
70 z_infa
= FPNumBaseRecord(width
, False, name
="z_infa")
71 z_infb
= FPNumBaseRecord(width
, False, name
="z_infb")
72 comb
+= z_zero
.zero(0)
74 comb
+= z_infa
.inf(a1
.s
)
75 comb
+= z_infb
.inf(b1
.s
)
78 comb
+= self
.o
.out_do_z
.eq(1)
80 # if a is NaN or b is NaN return NaN
82 comb
+= self
.o
.oz
.eq(z_nan
.v
)
84 # if a is inf return inf (or NaN)
85 with m
.Elif(a1
.is_inf
):
86 comb
+= self
.o
.oz
.eq(z_infa
.v
)
87 # if a is inf and signs don't match return NaN
89 comb
+= self
.o
.oz
.eq(z_nan
.v
)
91 # if b is inf return inf
92 with m
.Elif(b1
.is_inf
):
93 comb
+= self
.o
.oz
.eq(z_infb
.v
)
95 # if a is zero and b zero return signed-a/b
97 comb
+= self
.o
.oz
.eq(self
.i
.b
)
98 comb
+= self
.o
.oz
[-1].eq(absa
)
100 # if a is zero return b
101 with m
.Elif(a1
.is_zero
):
102 comb
+= self
.o
.oz
.eq(b1
.v
)
104 # if b is zero return a
105 with m
.Elif(b1
.is_zero
):
106 comb
+= self
.o
.oz
.eq(a1
.v
)
108 # if a equal to -b return zero (+ve zero)
110 comb
+= self
.o
.oz
.eq(z_zero
.v
)
112 # Denormalised Number checks next, so pass a/b data through
114 comb
+= self
.o
.out_do_z
.eq(0)
116 comb
+= self
.o
.ctx
.eq(self
.i
.ctx
)
121 class FPAddSpecialCasesDeNorm(PipeModBaseChain
):
122 """ special cases chain
126 """ links module to inputs and outputs
128 smod
= FPAddSpecialCasesMod(self
.pspec
)
129 dmod
= FPAddDeNormMod(self
.pspec
, True)