将4字节转换为有符号整数 [英] Convert 4 byte into a signed integer

问题描述

我正在尝试在浏览器中解析一个二进制文件.我有4个字节，代表一个32位带符号整数.
是否有将其转换为dart int的简便方法，还是我必须手动计算二进制补码的逆数?

I'm trying to parse a binary file in the browser. I have 4 bytes that represent a 32-bit signed integer.
Is there a straight forward way of converting this to a dart int, or do I have to calculate the inverse of two's complement manually?

谢谢

使用它进行手动转换:

  int readSignedInt() {
    int value = readUnsignedInt();
    if ((value & 0x80000000) > 0) {
      // This is a negative number.  Invert the bits and add 1
      value = (~value & 0xFFFFFFFF) + 1;

      // Add a negative sign
      value = -value;
    }
    return value;
  }

推荐答案

您可以使用 typed_data 库中的rel ="nofollow noreferrer"> ByteArray .

You can use ByteArray from typed_data library.

import 'dart:typed_data';

int fromBytesToInt32(int b3, int b2, int b1, int b0) {
  final int8List = new Int8List(4)
    ..[3] = b3
    ..[2] = b2
    ..[1] = b1
    ..[0] = b0;
  return int8List.asByteArray().getInt32(0);
}

void main() {
  assert(fromBytesToInt32(0x00, 0x00, 0x00, 0x00) == 0);
  assert(fromBytesToInt32(0x00, 0x00, 0x00, 0x01) == 1);
  assert(fromBytesToInt32(0xF0, 0x00, 0x00, 0x00) == -268435456);
}

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