C语言 如何将负的十六进制转换为十进制
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how to convert negative hexadecimal to decimal
提问by karim
hi I want to know how it is possible to convert a hexadecimal negative value (to complement encoding) to decimal, easily without converting hexadecimal to binary and then multiplying each bit in by a power of 2 and sums all the value to get the result, it takes too much time : example of number (32 bits) : 0xFFFFFE58
嗨，我想知道如何将十六进制负值（以补充编码）转换为十进制，而无需将十六进制转换为二进制，然后将每个位乘以 2 的幂并将所有值相加以获得结果，花费太多时间：数字示例（32 位）：0xFFFFFE58
so how can I do it?
那我该怎么做呢？
采纳答案by mch
without using a computer you can calculate it like this:
不用电脑，你可以这样计算：
0xFFFF FE58 = - 0x1A8 = -(1 * 162 + 10 * 16 + 8) = -(256 + 160 + 8) = -424
0xFFFF FE58is a negative number in 2's complement. To get the absolute value you have to invert all bits and add 1 in binary. You also can subtract this number from the first number out of range (0x1 0000 0000)
0xFFFF FE58是 2 的补码中的负数。要获得绝对值，您必须反转所有位并在二进制中加 1。您也可以从超出范围的第一个数字中减去此数字 (0x1 0000 0000)
0x100000000
-0x0FFFFFE58
=
0x0000001A8
now we know that your number is -0x1A8. now you have to add up the digits multiplied with their place value. 8 * 16^0 + A (which is 10) * 16^1 + 1 * 16^2 = 424. So the decimal value of your number is -424.
现在我们知道你的号码是-0x1A8。现在您必须将乘以它们的位值的数字相加。8 * 16^0 + A（即 10）* 16^1 + 1 * 16^2 = 424。所以你的数字的十进制值为 -424。
回答by shoham
do a calculation on the positive number, then convert to the negative with Two's complement.
对正数进行计算，然后用二进制补码转换为负数。
see explanation here for positive conversion from hexa to decimal:
有关从六进制到十进制的正转换，请参见此处的说明：
http://www.permadi.com/tutorial/numHexToDec/
http://www.permadi.com/tutorial/numHexToDec/
basically:
基本上：
- Get the right most digit of the hex number, call this digit the currentDigit.
- Make a variable, let's call it power. Set the value to 0.
- Multiply the current digit with (16^power), store the result.
- Increment power by 1.
- Set the the currentDigit to the previous digit of the hex number.
- Repeat from step 3 until all digits have been multiplied.
- Sum the result of step 3 to get the answer number.
- 获取十六进制数的最右边数字，将此数字称为 currentDigit。
- 制作一个变量，我们称之为权力。将该值设置为 0。
- 将当前数字乘以 (16^power)，存储结果。
- 将功率增加 1。
- 将 currentDigit 设置为十六进制数的前一位。
- 从第 3 步开始重复，直到所有数字都相乘。
- 将第 3 步的结果相加得到答案编号。
