Commit eb6a8e6a3bba061c4a7fb18f53976e1fb683c3d4 | zig

author	Ben Noordhuis <info@bnoordhuis.nl> 2018-06-20 21:51:18+02:00
committer	Andrew Kelley <andrew@ziglang.org> 2018-06-20 17:37:38-04:00
log	eb6a8e6a3bba061c4a7fb18f53976e1fb683c3d4
tree	137d90a657f1b6fe178f4eba4436c7ebfa2638b0
parent	4eca75c53b4679e7e31df1505d22a5b618a2d797

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

2 files changed, 23 insertions(+), 3 deletions(-)

src
- ir.cpp
test
- cases
  - math.zig

src/ir.cpp+9-3

 @@ -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);
+                zig_f128M_mod(&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);
                 return;
             default:
                 zig_unreachable();

test/cases/math.zig+14

...	@@ -434,6 +434,20 @@ test "comptime float rem int" {	...	@@ -434,6 +434,20 @@ test "comptime float rem int" {
434	}	434	}
435	}	435	}
436		436
		437	test "remainder division" {
		438	comptime remdiv(f32);
		439	comptime remdiv(f64);
		440	comptime remdiv(f128);
		441	remdiv(f32);
		442	remdiv(f64);
		443	remdiv(f128);
		444	}
		445
		446	fn remdiv(comptime T: type) void {
		447	assert(T(1) == T(1) % T(2));
		448	assert(T(1) == T(7) % T(3));
		449	}
		450
437	test "@sqrt" {	451	test "@sqrt" {
438	testSqrt(f64, 12.0);	452	testSqrt(f64, 12.0);
439	comptime testSqrt(f64, 12.0);	453	comptime testSqrt(f64, 12.0);