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C code 如何將24bits truncated 成16bits
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初級會員
 
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下面是一段程式我一直不懂的是它要把24bit 變成16bits
而大於16bit的它就把它刪掉 所以第一段code它應該要判段它的最高位元的如果為負號而且它比0x8000更負的話就都設定成 0x8000但是這段敘述 if((poserror.i[1] != 0xffff) || !(poserror.b[1] & 0x80)) 怎看都不太對勁，如果我是0xffff7fff 那poserror.b[1]=7f, 那!(poserror.b[1] & 0x80)為 ture所以進去然後被設成0xffff8000；就跟想的不太一樣 有人可以解惑嗎? 這是an718的一段程式應該沒錯 總覺得我不知那裡想錯了。附件有所有程式碼 //第一段code if (poserror.b[2] & 0x80)// If position error is negative. { poserror.b[3] = 0xff; // Sign-extend to 32 bits. if((poserror.i[1] != 0xffff) || !(poserror.b[1] & 0x80)) { poserror.i[1] = 0xffff;// Limit error to 16-bit signed //integer. poserror.i[0] = 0x8000; } else; } //第二段code else // If position error is positive. { poserror.b[3] = 0x00; if((poserror.i[1] != 0x0000) || (poserror.b[1] & 0x80)) { poserror.i[1] = 0x0000; // Limit error to 16-bit // signed integer. poserror.i[0] = 0x7fff; } else; Attach file: Link only for registered users
發表於: 2009/4/13 22:25
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