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Diffstat (limited to 'src/math/bits/example_math_test.go')
| -rw-r--r-- | src/math/bits/example_math_test.go | 202 |
1 files changed, 202 insertions, 0 deletions
diff --git a/src/math/bits/example_math_test.go b/src/math/bits/example_math_test.go new file mode 100644 index 0000000..4bb466f --- /dev/null +++ b/src/math/bits/example_math_test.go @@ -0,0 +1,202 @@ +// Copyright 2021 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package bits_test + +import ( + "fmt" + "math/bits" +) + +func ExampleAdd32() { + // First number is 33<<32 + 12 + n1 := []uint32{33, 12} + // Second number is 21<<32 + 23 + n2 := []uint32{21, 23} + // Add them together without producing carry. + d1, carry := bits.Add32(n1[1], n2[1], 0) + d0, _ := bits.Add32(n1[0], n2[0], carry) + nsum := []uint32{d0, d1} + fmt.Printf("%v + %v = %v (carry bit was %v)\n", n1, n2, nsum, carry) + + // First number is 1<<32 + 2147483648 + n1 = []uint32{1, 0x80000000} + // Second number is 1<<32 + 2147483648 + n2 = []uint32{1, 0x80000000} + // Add them together producing carry. + d1, carry = bits.Add32(n1[1], n2[1], 0) + d0, _ = bits.Add32(n1[0], n2[0], carry) + nsum = []uint32{d0, d1} + fmt.Printf("%v + %v = %v (carry bit was %v)\n", n1, n2, nsum, carry) + // Output: + // [33 12] + [21 23] = [54 35] (carry bit was 0) + // [1 2147483648] + [1 2147483648] = [3 0] (carry bit was 1) +} + +func ExampleAdd64() { + // First number is 33<<64 + 12 + n1 := []uint64{33, 12} + // Second number is 21<<64 + 23 + n2 := []uint64{21, 23} + // Add them together without producing carry. + d1, carry := bits.Add64(n1[1], n2[1], 0) + d0, _ := bits.Add64(n1[0], n2[0], carry) + nsum := []uint64{d0, d1} + fmt.Printf("%v + %v = %v (carry bit was %v)\n", n1, n2, nsum, carry) + + // First number is 1<<64 + 9223372036854775808 + n1 = []uint64{1, 0x8000000000000000} + // Second number is 1<<64 + 9223372036854775808 + n2 = []uint64{1, 0x8000000000000000} + // Add them together producing carry. + d1, carry = bits.Add64(n1[1], n2[1], 0) + d0, _ = bits.Add64(n1[0], n2[0], carry) + nsum = []uint64{d0, d1} + fmt.Printf("%v + %v = %v (carry bit was %v)\n", n1, n2, nsum, carry) + // Output: + // [33 12] + [21 23] = [54 35] (carry bit was 0) + // [1 9223372036854775808] + [1 9223372036854775808] = [3 0] (carry bit was 1) +} + +func ExampleSub32() { + // First number is 33<<32 + 23 + n1 := []uint32{33, 23} + // Second number is 21<<32 + 12 + n2 := []uint32{21, 12} + // Sub them together without producing carry. + d1, carry := bits.Sub32(n1[1], n2[1], 0) + d0, _ := bits.Sub32(n1[0], n2[0], carry) + nsum := []uint32{d0, d1} + fmt.Printf("%v - %v = %v (carry bit was %v)\n", n1, n2, nsum, carry) + + // First number is 3<<32 + 2147483647 + n1 = []uint32{3, 0x7fffffff} + // Second number is 1<<32 + 2147483648 + n2 = []uint32{1, 0x80000000} + // Sub them together producing carry. + d1, carry = bits.Sub32(n1[1], n2[1], 0) + d0, _ = bits.Sub32(n1[0], n2[0], carry) + nsum = []uint32{d0, d1} + fmt.Printf("%v - %v = %v (carry bit was %v)\n", n1, n2, nsum, carry) + // Output: + // [33 23] - [21 12] = [12 11] (carry bit was 0) + // [3 2147483647] - [1 2147483648] = [1 4294967295] (carry bit was 1) +} + +func ExampleSub64() { + // First number is 33<<64 + 23 + n1 := []uint64{33, 23} + // Second number is 21<<64 + 12 + n2 := []uint64{21, 12} + // Sub them together without producing carry. + d1, carry := bits.Sub64(n1[1], n2[1], 0) + d0, _ := bits.Sub64(n1[0], n2[0], carry) + nsum := []uint64{d0, d1} + fmt.Printf("%v - %v = %v (carry bit was %v)\n", n1, n2, nsum, carry) + + // First number is 3<<64 + 9223372036854775807 + n1 = []uint64{3, 0x7fffffffffffffff} + // Second number is 1<<64 + 9223372036854775808 + n2 = []uint64{1, 0x8000000000000000} + // Sub them together producing carry. + d1, carry = bits.Sub64(n1[1], n2[1], 0) + d0, _ = bits.Sub64(n1[0], n2[0], carry) + nsum = []uint64{d0, d1} + fmt.Printf("%v - %v = %v (carry bit was %v)\n", n1, n2, nsum, carry) + // Output: + // [33 23] - [21 12] = [12 11] (carry bit was 0) + // [3 9223372036854775807] - [1 9223372036854775808] = [1 18446744073709551615] (carry bit was 1) +} + +func ExampleMul32() { + // First number is 0<<32 + 12 + n1 := []uint32{0, 12} + // Second number is 0<<32 + 12 + n2 := []uint32{0, 12} + // Multiply them together without producing overflow. + hi, lo := bits.Mul32(n1[1], n2[1]) + nsum := []uint32{hi, lo} + fmt.Printf("%v * %v = %v\n", n1[1], n2[1], nsum) + + // First number is 0<<32 + 2147483648 + n1 = []uint32{0, 0x80000000} + // Second number is 0<<32 + 2 + n2 = []uint32{0, 2} + // Multiply them together producing overflow. + hi, lo = bits.Mul32(n1[1], n2[1]) + nsum = []uint32{hi, lo} + fmt.Printf("%v * %v = %v\n", n1[1], n2[1], nsum) + // Output: + // 12 * 12 = [0 144] + // 2147483648 * 2 = [1 0] +} + +func ExampleMul64() { + // First number is 0<<64 + 12 + n1 := []uint64{0, 12} + // Second number is 0<<64 + 12 + n2 := []uint64{0, 12} + // Multiply them together without producing overflow. + hi, lo := bits.Mul64(n1[1], n2[1]) + nsum := []uint64{hi, lo} + fmt.Printf("%v * %v = %v\n", n1[1], n2[1], nsum) + + // First number is 0<<64 + 9223372036854775808 + n1 = []uint64{0, 0x8000000000000000} + // Second number is 0<<64 + 2 + n2 = []uint64{0, 2} + // Multiply them together producing overflow. + hi, lo = bits.Mul64(n1[1], n2[1]) + nsum = []uint64{hi, lo} + fmt.Printf("%v * %v = %v\n", n1[1], n2[1], nsum) + // Output: + // 12 * 12 = [0 144] + // 9223372036854775808 * 2 = [1 0] +} + +func ExampleDiv32() { + // First number is 0<<32 + 6 + n1 := []uint32{0, 6} + // Second number is 0<<32 + 3 + n2 := []uint32{0, 3} + // Divide them together. + quo, rem := bits.Div32(n1[0], n1[1], n2[1]) + nsum := []uint32{quo, rem} + fmt.Printf("[%v %v] / %v = %v\n", n1[0], n1[1], n2[1], nsum) + + // First number is 2<<32 + 2147483648 + n1 = []uint32{2, 0x80000000} + // Second number is 0<<32 + 2147483648 + n2 = []uint32{0, 0x80000000} + // Divide them together. + quo, rem = bits.Div32(n1[0], n1[1], n2[1]) + nsum = []uint32{quo, rem} + fmt.Printf("[%v %v] / %v = %v\n", n1[0], n1[1], n2[1], nsum) + // Output: + // [0 6] / 3 = [2 0] + // [2 2147483648] / 2147483648 = [5 0] +} + +func ExampleDiv64() { + // First number is 0<<64 + 6 + n1 := []uint64{0, 6} + // Second number is 0<<64 + 3 + n2 := []uint64{0, 3} + // Divide them together. + quo, rem := bits.Div64(n1[0], n1[1], n2[1]) + nsum := []uint64{quo, rem} + fmt.Printf("[%v %v] / %v = %v\n", n1[0], n1[1], n2[1], nsum) + + // First number is 2<<64 + 9223372036854775808 + n1 = []uint64{2, 0x8000000000000000} + // Second number is 0<<64 + 9223372036854775808 + n2 = []uint64{0, 0x8000000000000000} + // Divide them together. + quo, rem = bits.Div64(n1[0], n1[1], n2[1]) + nsum = []uint64{quo, rem} + fmt.Printf("[%v %v] / %v = %v\n", n1[0], n1[1], n2[1], nsum) + // Output: + // [0 6] / 3 = [2 0] + // [2 9223372036854775808] / 9223372036854775808 = [5 0] +} |