range: Check zero-divide in ranges

When dividing by a range that contains zero, emit a range with
infinities.

Signed-off-by: Christophe de Dinechin <[email protected]>

Author: c3d

src/range.cc

@@ -346,10 +346,14 @@ range_g operator*(range_r x, range_r y)
 {
     if (!x|| !y)
         return nullptr;
-    algebraic_g a = x->lo() * y->lo();
-    algebraic_g b = x->lo() * y->hi();
-    algebraic_g c = x->hi() * y->lo();
-    algebraic_g d = x->hi() * y->hi();
+    algebraic_g xlo = x->lo();
+    algebraic_g xhi = x->hi();
+    algebraic_g ylo = y->lo();
+    algebraic_g yhi = y->hi();
+    algebraic_g a = xlo * ylo;
+    algebraic_g b = xlo * yhi;
+    algebraic_g c = xhi * ylo;
+    algebraic_g d = xhi * yhi;
 
     range::sort(a, b);
     range::sort(a, c);
@@ -367,10 +371,21 @@ range_g operator/(range_r x, range_r y)
 {
     if (!x|| !y)
         return nullptr;
-    algebraic_g a = x->lo() / y->lo();
-    algebraic_g b = x->lo() / y->hi();
-    algebraic_g c = x->hi() / y->lo();
-    algebraic_g d = x->hi() / y->hi();
+    algebraic_g xlo = x->lo();
+    algebraic_g xhi = x->hi();
+    algebraic_g ylo = y->lo();
+    algebraic_g yhi = y->hi();
+    if (ylo->is_zero(false) || yhi->is_zero(false) ||
+        ylo->is_negative(false) != yhi->is_negative())
+    {
+        ylo = rt.infinity(true);
+        yhi = rt.infinity(false);
+        return range::make(y->type(), ylo, yhi);
+    }
+    algebraic_g a = xlo / ylo;
+    algebraic_g b = xlo / yhi;
+    algebraic_g c = xhi / ylo;
+    algebraic_g d = xhi / yhi;
 
     range::sort(a, b);
     range::sort(a, c);

src/tests.cc

@@ -5389,11 +5389,13 @@ void tests::range_types()
     step("Multiply delta ranges")
         .test(CLEAR, "1±3 2±5", NOSHIFT, MUL).expect("7±21");
     step("Divide delta ranges")
-        .test(CLEAR, "1±3 2±5", NOSHIFT, DIV).expect("-¹/₃±1");
+        .test(CLEAR, "10±3 20±5", NOSHIFT, DIV).expect("⁴³/₇₅±²²/₇₅")
+        .test(CLEAR, "1±3 2±5", NOSHIFT, DIV).expect("−∞…∞");
     step("Power delta ranges")
         .test(CLEAR, "2±1 5±2", NOSHIFT, ID_pow).expect("1 094.±1 093.");
     step("Invert delta ranges")
-        .test(CLEAR, "1±3", NOSHIFT, ID_inv).expect("-¹/₈±³/₈");
+        .test(CLEAR, "10±3", NOSHIFT, ID_inv).expect("¹⁰/₉₁±³/₉₁")
+        .test(CLEAR, "1±3", NOSHIFT, ID_inv).expect("−∞…∞");
     step("Negate delta ranges")
         .test(CLEAR, "1±3", ENTER, ID_neg).expect("-1±3");
 
@@ -5415,7 +5417,8 @@ void tests::range_types()
     step("Multiply delta ranges")
         .test(CLEAR, "5 1±3", NOSHIFT, MUL).expect("5±15");
     step("Divide delta ranges")
-        .test(CLEAR, "5 1±3", NOSHIFT, DIV).expect("-⁵/₈±1 ⁷/₈");
+        .test(CLEAR, "5 10±3", NOSHIFT, DIV).expect("⁵⁰/₉₁±¹⁵/₉₁")
+        .test(CLEAR, "5 1±3", NOSHIFT, DIV).expect("−∞…∞");
     step("Power delta ranges")
         .test(CLEAR, "5 1±3", NOSHIFT, ID_pow).expect("312.52±312.48");