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Task/Safe-addition/Nim/safe-addition.nim

@@ -0,0 +1,20 @@
+import posix, strutils
+
+proc `++`(a, b: float): tuple[lower, upper: float] =
+  let
+    a {.volatile.} = a
+    b {.volatile.} = b
+    orig = fegetround()
+  discard fesetround FE_DOWNWARD
+  result.lower = a + b
+  discard fesetround FE_UPWARD
+  result.upper = a + b
+  discard fesetround orig
+
+proc ff(a: float): string = a.formatFloat(ffDefault, 17)
+
+for x, y in [(1.0, 2.0), (0.1, 0.2), (1e100, 1e-100), (1e308, 1e308)].items:
+  let (d,u) = x ++ y
+  echo x.ff, " + ", y.ff, " ="
+  echo "    [", d.ff, ", ", u.ff, "]"
+  echo "    size ", (u - d).ff, "\n"