zig

commit eb6a8e6a3bba061c4a7fb18f53976e1fb683c3d4 (tree)
parent 4eca75c53b4679e7e31df1505d22a5b618a2d797
Author: Ben Noordhuis <info@bnoordhuis.nl>
Date:   Wed, 20 Jun 2018 21:51:18 +0200

fix f128 remainder division bug

The modulo operation computed rem(b+rem(a,b), b) which produces -1
for a=1 and b=2.

Switch to a - b * trunc(a/b) which produces the expected result, 1.

closes #1137

Diffstat:
M
src/ir.cpp
 | 
12
+++++++++---
M
test/cases/math.zig
 | 
14
++++++++++++++

2 files changed, 23 insertions(+), 3 deletions(-)
diff --git a/src/ir.cpp b/src/ir.cpp
@@ -7710,6 +7710,14 @@ static void float_rem(ConstExprValue *out_val, ConstExprValue *op1, ConstExprVal
     }
 }
 
+// c = a - b * trunc(a / b)
+static void zig_f128M_mod(const float128_t* a, const float128_t* b, float128_t* c) {
+    f128M_div(a, b, c);
+    f128M_roundToInt(c, softfloat_round_min, true, c);
+    f128M_mul(b, c, c);
+    f128M_sub(a, c, c);
+}
+
 static void float_mod(ConstExprValue *out_val, ConstExprValue *op1, ConstExprValue *op2) {
     assert(op1->type == op2->type);
     out_val->type = op1->type;
@@ -7724,9 +7732,7 @@ static void float_mod(ConstExprValue *out_val, ConstExprValue *op1, ConstExprVal
                 out_val->data.x_f64 = fmod(fmod(op1->data.x_f64, op2->data.x_f64) + op2->data.x_f64, op2->data.x_f64);
                 return;
             case 128:
-                f128M_rem(&op1->data.x_f128, &op2->data.x_f128, &out_val->data.x_f128);
-                f128M_add(&out_val->data.x_f128, &op2->data.x_f128, &out_val->data.x_f128);
-                f128M_rem(&out_val->data.x_f128, &op2->data.x_f128, &out_val->data.x_f128);
+                zig_f128M_mod(&op1->data.x_f128, &op2->data.x_f128, &out_val->data.x_f128);
                 return;
             default:
                 zig_unreachable();
diff --git a/test/cases/math.zig b/test/cases/math.zig
@@ -434,6 +434,20 @@ test "comptime float rem int" {
     }
 }
 
+test "remainder division" {
+    comptime remdiv(f32);
+    comptime remdiv(f64);
+    comptime remdiv(f128);
+    remdiv(f32);
+    remdiv(f64);
+    remdiv(f128);
+}
+
+fn remdiv(comptime T: type) void {
+    assert(T(1) == T(1) % T(2));
+    assert(T(1) == T(7) % T(3));
+}
+
 test "@sqrt" {
     testSqrt(f64, 12.0);
     comptime testSqrt(f64, 12.0);