github.com/datastax/go-cassandra-native-protocol@v0.0.0-20220706104457-5e8aad05cf90/datacodec/math.go (about)

     1  // Copyright 2021 DataStax
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package datacodec
    16  
    17  import (
    18  	"math"
    19  )
    20  
    21  // Adapted from java.lang.Math#addExact(long, long).
    22  // Returns the sum of its arguments, and a boolean indicating whether the sum overflowed.
    23  func addExact(x, y int64) (int64, bool) {
    24  	r := x + y
    25  	if ((x ^ r) & (y ^ r)) < 0 {
    26  		return 0, true
    27  	}
    28  	return r, false
    29  }
    30  
    31  // Adapted from:
    32  // https://stackoverflow.com/questions/50744681/testing-overflow-in-integer-multiplication.
    33  // Returns the product of its arguments, and a boolean indicating whether the product overflowed.
    34  // Another interesting implementation can be found in java.lang.Math#multiplyExact(long, long).
    35  func multiplyExact(x, y int64) (int64, bool) {
    36  	if x == 0 || y == 0 || x == 1 || y == 1 {
    37  		return x * y, false
    38  	} else if x == math.MinInt64 || y == math.MinInt64 {
    39  		return 0, true
    40  	} else {
    41  		r := x * y
    42  		if r/y != x {
    43  			return 0, true
    44  		}
    45  		return r, false
    46  	}
    47  }
    48  
    49  // Adapted from java.lang.Math#floorDiv(int, int).
    50  // Returns the largest (closest to positive infinity) long value that is less than or equal to the algebraic quotient.
    51  // There is one special case, if the dividend is the Long.MIN_VALUE and the divisor is -1, then integer overflow occurs
    52  // and the result is equal to the Long.MIN_VALUE.
    53  // Normal integer division operates under the round to zero rounding mode (truncation). This operation instead acts
    54  // under the round toward negative infinity (floor) rounding mode. The floor rounding mode gives different results than
    55  // truncation when the exact result is negative.
    56  func floorDiv(x, y int64) int64 {
    57  	r := x / y
    58  	// if the signs are different and modulo not zero, round down
    59  	if (x^y) < 0 && (r*y != x) {
    60  		r--
    61  	}
    62  	return r
    63  }
    64  
    65  // Adapted from java.lang.Math#floorMod(int, int).
    66  // Returns the floor modulus of the long arguments.
    67  // The floor modulus is x - (floorDiv(x, y) * y), has the same sign as the divisor y, and is in the range of
    68  // -abs(y) < r < +abs(y).
    69  func floorMod(x, y int64) int64 {
    70  	return x - floorDiv(x, y)*y
    71  }