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Question

我使用以下代码检查位数25值是0还是1:

volatile unsigned int * regAddr;
unsigned int regval;

regAddress = (unsigned int *) 0xD2009010;   //This is a valid address of register

regVal = *regAddress;   //The return value here is 0xFE008000

if (!(regVal & 0x4000000))     //For the mentioned return value, I thought the condition will be different then 0 and so used '!' to convert the value
    the bit is 0;
else
    the bit is 1;

此代码无法正常工作,我无法弄清楚原因.帮助任何人？提前致谢

Answer 1

获得第25位的可靠方法是:

if (!(regVal & (1 << 24) ))

或者,如果您愿意:

#define BIT_25 (1 << 24)  // the first-bit, shifted over 24 more times.

if (!(regVal & BIT_25 ))

有些人提出"位数25"是不明确的,这取决于你是将0x01视为第一位还是第零位.

自己决定适合您的计划.
但无论如何,0x4000000都是对的.