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fix f128 remainder division bug

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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
This commit is contained in:
Ben Noordhuis 2018-06-20 21:51:18 +02:00 committed by Andrew Kelley
parent 4eca75c53b
commit eb6a8e6a3b
2 changed files with 23 additions and 3 deletions
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12
src/ir.cpp
View File

@ -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();

14
test/cases/math.zig
View File

@ -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);