Revert "Attempt to resolve https://github.com/graphcore-research/gfloat/pull/24/files#r1628019184"

This reverts commit 61c3b494b36663a35efe7d0af18b3b9f28030a14.

Author: awf

src/gfloat/round.py

@@ -73,34 +73,40 @@ def round_float(
 
         fsignificand = vpos * 2.0**-expval
 
-        # Round.
+        # Round
         isignificand = math.floor(fsignificand)
         delta = fsignificand - isignificand
-
-        # Is the integer codepoint odd or even?
-        if rnd == RoundMode.TiesToEven:
-            code_is_odd = _isodd(isignificand)
-            if fi.precision == 1:  # When precision == 1, also check exponent.
-                code_is_odd = isignificand != 0 and _isodd(expval + bias)
-
-        # Rounded value will be either isignificand or isignificand+1.
         if (
-            (
-                rnd == RoundMode.TiesToEven
-                and (delta > 0.5 or delta == 0.5 and code_is_odd)
-            )
-            or (rnd == RoundMode.TiesToAway and delta >= 0.5)
-            or (rnd == RoundMode.TowardPositive and not sign and delta > 0)
+            (rnd == RoundMode.TowardPositive and not sign and delta > 0)
             or (rnd == RoundMode.TowardNegative and sign and delta > 0)
+            or (rnd == RoundMode.TiesToAway and delta >= 0.5)
+            or (rnd == RoundMode.TiesToEven and delta > 0.5)
+            or (rnd == RoundMode.TiesToEven and delta == 0.5 and _isodd(isignificand))
         ):
             isignificand += 1
-            if fi.precision == 1 and isignificand == 2:
-                # Special case for p = 1: carry overflowed significand to exponent.
-                # (Not needed for p>1 as we are reconstructing, not encoding)
-                isignificand = 1
-                expval += 1
 
-        # Reconstruct from integer significand and exponent
+        ## Special case for Precision=1, all-log format with zero.
+        if fi.precision == 1:
+            # The logic is simply duplicated for clarity of reading.
+            isignificand = math.floor(fsignificand)
+            code_is_odd = isignificand != 0 and _isodd(expval + bias)
+            if (
+                (rnd == RoundMode.TowardPositive and not sign and delta > 0)
+                or (rnd == RoundMode.TowardNegative and sign and delta > 0)
+                or (rnd == RoundMode.TiesToAway and delta >= 0.5)
+                or (rnd == RoundMode.TiesToEven and delta > 0.5)
+                or (rnd == RoundMode.TiesToEven and delta == 0.5 and code_is_odd)
+            ):
+                # Go to nextUp.
+                # Increment isignificand if zero,
+                # else increment exponent
+                if isignificand == 0:
+                    isignificand = 1
+                else:
+                    assert isignificand == 1
+                    expval += 1
+        ## End special case for Precision=1.
+
         result = isignificand * (2.0**expval)
 
     if result == 0: