From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Tue, 19 Feb 2019 11:23:22 +0000 (+0000)
Subject: take out FP16 non-canonical NaN weirdness for now
X-Git-Tag: ls180-24jan2020~1867
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=ee00fd20e0d3717ac32227c6ecad308ede7d99e5;p=ieee754fpu.git

take out FP16 non-canonical NaN weirdness for now
---

diff --git a/src/add/nmigen_add_experiment.py b/src/add/nmigen_add_experiment.py
index 6baaad66..ec4ebb84 100644
--- a/src/add/nmigen_add_experiment.py
+++ b/src/add/nmigen_add_experiment.py
@@ -55,25 +55,33 @@ class FPADD(FPBase):
 
             with m.State("special_cases"):
 
-                # if a is zero and b is NaN return -b
-                with m.If(a.is_zero() & (a.s==0) & b.is_nan()):
+                # if a is NaN or b is NaN return NaN
+                with m.If(a.is_nan() | b.is_nan()):
                     m.next = "put_z"
-                    m.d.sync += z.create(b.s, b.e, Cat(b.m[3:-2], ~b.m[0]))
-
-                # if b is zero and a is NaN return -a
-                with m.Elif(b.is_zero() & (b.s==0) & a.is_nan()):
-                    m.next = "put_z"
-                    m.d.sync += z.create(a.s, a.e, Cat(a.m[3:-2], ~a.m[0]))
-
-                # if a is -zero and b is NaN return -b
-                with m.Elif(a.is_zero() & (a.s==1) & b.is_nan()):
-                    m.next = "put_z"
-                    m.d.sync += z.create(a.s & b.s, b.e, Cat(b.m[3:-2], 1))
-
-                # if b is -zero and a is NaN return -a
-                with m.Elif(b.is_zero() & (b.s==1) & a.is_nan()):
-                    m.next = "put_z"
-                    m.d.sync += z.create(a.s & b.s, a.e, Cat(a.m[3:-2], 1))
+                    m.d.sync += z.nan(1)
+
+                # XXX WEIRDNESS for FP16 non-canonical NaN handling
+                # under review
+
+                ## if a is zero and b is NaN return -b
+                #with m.If(a.is_zero() & (a.s==0) & b.is_nan()):
+                #    m.next = "put_z"
+                #    m.d.sync += z.create(b.s, b.e, Cat(b.m[3:-2], ~b.m[0]))
+
+                ## if b is zero and a is NaN return -a
+                #with m.Elif(b.is_zero() & (b.s==0) & a.is_nan()):
+                #    m.next = "put_z"
+                #    m.d.sync += z.create(a.s, a.e, Cat(a.m[3:-2], ~a.m[0]))
+
+                ## if a is -zero and b is NaN return -b
+                #with m.Elif(a.is_zero() & (a.s==1) & b.is_nan()):
+                #    m.next = "put_z"
+                #    m.d.sync += z.create(a.s & b.s, b.e, Cat(b.m[3:-2], 1))
+
+                ## if b is -zero and a is NaN return -a
+                #with m.Elif(b.is_zero() & (b.s==1) & a.is_nan()):
+                #    m.next = "put_z"
+                #    m.d.sync += z.create(a.s & b.s, a.e, Cat(a.m[3:-2], 1))
 
                 # if a is inf return inf (or NaN)
                 with m.Elif(a.is_inf()):
diff --git a/src/add/test_add.py b/src/add/test_add.py
index bb419049..cc0ff98a 100644
--- a/src/add/test_add.py
+++ b/src/add/test_add.py
@@ -13,6 +13,7 @@ from unit_test_single import (get_mantissa, get_exponent, get_sign, is_nan,
                                 run_edge_cases, run_corner_cases)
 
 def testbench(dut):
+    yield from check_case(dut, 0xFFFFFFFF, 0xC63B800A, 0xFFC00000)
     yield from check_case(dut, 0xFF800000, 0x7F800000, 0xFFC00000)
     #yield from check_case(dut, 0xFF800000, 0x7F800000, 0x7FC00000)
     yield from check_case(dut, 0x7F800000, 0xFF800000, 0xFFC00000)
@@ -31,7 +32,6 @@ def testbench(dut):
     yield from check_case(dut, 0xC2BA8A3D, 0x463B800A, 0x463A0AF6)
     yield from check_case(dut, 0xC63B800A, 0x42BA8A3D, 0xC63A0AF6)
     yield from check_case(dut, 0x42BA8A3D, 0xC63B800A, 0xC63A0AF6)
-    yield from check_case(dut, 0xFFFFFFFF, 0xC63B800A, 0xFFC00000)
     yield from check_case(dut, 0x7F800000, 0x00000000, 0x7F800000)
     yield from check_case(dut, 0x00000000, 0x7F800000, 0x7F800000)
     yield from check_case(dut, 0xFF800000, 0x00000000, 0xFF800000)