{"resolved":true,"match_type":"uuid","source_type":"original_book","book_id":"38270854-596f-4a26-8183-db8c968c6020","title":"编码 隐匿在计算机软硬件背后的语言","author":null,"edition":null,"publisher":null,"year":null,"isbn":"9787121181184","requested_by":"printed_page","book":{"source_type":"original_book","book_id":"38270854-596f-4a26-8183-db8c968c6020","id":"38270854-596f-4a26-8183-db8c968c6020","uuid":"38270854-596f-4a26-8183-db8c968c6020","title":"编码 隐匿在计算机软硬件背后的语言","normalized_title":"编码隐匿在计算机软硬件背后的语言","author":null,"edition":null,"publisher":null,"year":null,"isbn":"9787121181184","isbns":["9787121181184","0123456789","6044921875","3039331000","0000000000","0000000000000"],"parsed":true,"ai_readable":true,"document_type":"book","page_count":438,"navigation_url":"https://workshop.closeclaw.top/ai/book/38270854-596f-4a26-8183-db8c968c6020","title_url":"https://workshop.closeclaw.top/ai/title/%E7%BC%96%E7%A0%81%20%E9%9A%90%E5%8C%BF%E5%9C%A8%E8%AE%A1%E7%AE%97%E6%9C%BA%E8%BD%AF%E7%A1%AC%E4%BB%B6%E8%83%8C%E5%90%8E%E7%9A%84%E8%AF%AD%E8%A8%80","fixed_page_url_template":"https://workshop.closeclaw.top/ai/book/38270854-596f-4a26-8183-db8c968c6020/page/{printed_page}","path_api_url_template":"https://workshop.closeclaw.top/api/ai/book/38270854-596f-4a26-8183-db8c968c6020/page/{printed_page}","read_url":"https://workshop.closeclaw.top/api/ai/read/38270854-596f-4a26-8183-db8c968c6020","page_url":"https://workshop.closeclaw.top/api/ai/books/38270854-596f-4a26-8183-db8c968c6020/page","search_url":"https://workshop.closeclaw.top/api/ai/books/38270854-596f-4a26-8183-db8c968c6020/search"},"page":{"printed_page":154,"pdf_page":170,"physical_index":170,"physical_index_base":0,"printed_page_status":"recognized","page_sha256":"e30a16816133e2f1f74ca6a17633c753aea8f0e84a7406ea536261b6c6c4c7bd"},"chapter":"编码隐匿在计算机软硬件背后的语言","content":"如上图所示，这个开关向下断开时表示选择加法运算，反之向上接通则表示选择减法运算。此外，右侧的8个灯泡用于表示计算结果。这里，第9个灯泡表示“上溢/下溢”。这个灯泡表明了正在计算的数字是一个不能用8个灯泡来表示的数字。如果在加法中得到了大于255（上溢，overflow）或在减法中得到了负数（下溢，underflow）这个灯泡就会发光。当减数大于被减数的时候，就会得到一个负数。\n\n加法器中新增的主要部分就是一个用来求8位二进制数对1补数的电路。之前提到，二进制数对1求补数相当于对其每位取反，因此我们计算8位二进制数补数的时候可以简单地应用8个反向器。\n\n问题是，该电路只会对输入求反，而我们要的是一台既能做加法又能做减法的机器，因此就要求该电路当且仅当进行减法运算时才实现反转。电路可以改造为如下图所示。\n\n标记为“取反”的信号将被输入到每一个异或门中。回想一下异或门的工作方式，如下表所示。\n\n因此，如果“取反”信号是0，则8个异或门输出与输入相同。例如，如果输入是01100001，那么输出也为01100001。如果“取反”信号为1，则输出信号反置。例如，如果输入为01100001，输出则为10011110。\n\n编码隐匿在计算机软硬件背后的语言\n\n154","previous_page":153,"next_page":155}