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Copy path10-01_integer_division_by_constant_signed_test.go
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10-01_integer_division_by_constant_signed_test.go
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package hd_test
import (
"fmt"
"testing"
hd "github.com/nikolaydubina/go-hackers-delight"
)
func ExampleDivSignedPowTwo_fixed5() {
fmt.Println(hd.DivSignedPowTwo_fixed5(96))
// Output: 3
}
func FuzzDivPow2(f *testing.F) {
for _, u := range fuzzInt32 {
f.Add(u, uint8(2))
}
f.Fuzz(func(t *testing.T, x int32, k uint8) {
k = k % 32
if k == 0 {
k++
}
Q := x / (1 << k)
R := x % (1 << k)
// preventing Go sign conversion bit.
if k == 31 {
Q = -Q
}
vs := []int32{
hd.DivSignedPowTwo(x, int(k)),
hd.DivSignedPowTwo2(x, int(k)),
}
for i, v := range vs {
if v != Q {
t.Errorf("%d: (%d, %d) = %d; want %d", i, x, k, v, Q)
}
}
if q, r := hd.DivModSignedPowTwo(x, int(k)); Q != q || R != r {
t.Errorf("DivModPowTwo(%d, %d) = (%d, %d); want (%d, %d)", x, k, q, r, Q, R)
}
})
}
func FuzzDivMod_int32(f *testing.F) {
for _, u := range fuzzInt32 {
f.Add(u)
}
f.Fuzz(func(t *testing.T, x int32) {
t.Run("mod3", func(t *testing.T) {
Q, R := x/3, x%3
if q, r := hd.DivMod3Signed(x); q != Q || r != R {
t.Errorf("DivMod3(%d) = got(%d, %d); want (%d, %d)", x, q, r, Q, R)
}
if q, r := hd.DivMod3Signed2(x); q != Q || r != R {
t.Errorf("DivMod3(%d) = got(%d, %d); want (%d, %d)", x, q, r, Q, R)
}
if q, r := hd.DivModConstSigned(x, 3); q != Q || r != R {
t.Errorf("DivMod3(%d) = got(%d, %d); want (%d, %d)", x, q, r, Q, R)
}
})
t.Run("mod5", func(t *testing.T) {
q, r := x/5, x%5
if Q, R := hd.DivMod5Signed(x); q != Q || r != R {
t.Errorf("DivMod5(%d) = got(%d, %d); want (%d, %d)", x, Q, R, q, r)
}
if Q, R := hd.DivModConstSigned(x, 5); q != Q || r != R {
t.Errorf("DivMod5(%d) = got(%d, %d); want (%d, %d)", x, Q, R, q, r)
}
})
t.Run("mod7", func(t *testing.T) {
Q, R := x/7, x%7
if q, r := hd.DivMod7Signed(x); q != Q || r != R {
t.Errorf("DivMod7(%d) = got(%d, %d); want (%d, %d)", x, q, r, Q, R)
}
if q, r := hd.DivModConstSigned(x, 7); q != Q || r != R {
t.Errorf("DivMod7(%d) = got(%d, %d); want (%d, %d)", x, q, r, Q, R)
}
})
})
}
func int32FromHex(x uint32) int32 { return int32(x) }
func TestMagicSigned(t *testing.T) {
type tc struct {
M int32
s int32
}
tests := map[int32]tc{
-5: {M: int32FromHex(0x9999_9999), s: 1},
-3: {M: 0x5555_5555, s: 1},
3: {M: 0x5555_5556, s: 0},
5: {M: 0x6666_6667, s: 1},
6: {M: 0x2AAA_AAAB, s: 0},
7: {M: int32FromHex(0x9249_2493), s: 2},
9: {M: 0x38E3_8E39, s: 1},
10: {M: 0x6666_6667, s: 2},
11: {M: 0x2E8B_A2E9, s: 1},
12: {M: 0x2AAA_AAAB, s: 1},
25: {M: 0x51EB_851F, s: 3},
125: {M: 0x1062_4DD3, s: 3},
625: {M: 0x68DB_8BAD, s: 8},
}
for _, k := range []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10} {
tests[-1<<k] = tc{M: 0x7FFF_FFFF, s: int32(k - 1)}
tests[+1<<k] = tc{M: int32FromHex(0x8000_0001), s: int32(k - 1)}
}
for d, tc := range tests {
t.Run(fmt.Sprintf("%v", d), func(t *testing.T) {
M, s := hd.DivModConstSignedMagic(d)
if M != tc.M || s != tc.s {
t.Errorf("MagicSigned(%d) = (%x, %d); want (%x, %d)", d, M, s, tc.M, tc.s)
}
})
}
}
func FuzzDivModSignedConst(f *testing.F) {
for _, x := range fuzzInt32 {
for _, y := range fuzzInt32 {
f.Add(x, y)
}
}
f.Fuzz(func(t *testing.T, x, y int32) {
if y > -2 && y < 2 {
t.Skip()
}
if y == 0 {
t.Skip()
}
// TODO: why integer signed division by negative constants is not working?
if y < 0 {
t.Skip()
}
Q, R := x/y, x%y
if q, r := hd.DivModConstSigned(x, y); Q != q || R != r {
t.Errorf("DivModConst(%d, %d) = (%d, %d); want (%d, %d)", x, y, q, r, Q, R)
}
})
}