unsigned

Obviously, Java doesn't support unsigned number types natively, and that's not going to change soon (comments starting in 2002). However, when working with databases, such as MySQL, they may come in handy every now and then. There are a lot of questions dealing with how to simulate unsigned numbers. For example: unsigned short in java Java: Unsigned numbers Understanding Java unsigned numbers All of them superficially describe how it could be done. But is there any library actually going all the way and implementing suitable wrappers for UByte , UShort , UInteger , ULong ? Preferably, those

-1 can be represented in 4 bit binary as (2's complement) 1111 15 is also represented as 1111. So, how does CPU differentiate between 15 and -1 when it gets values from memory? The CPU doesn't care whether a byte holds -1 or 15 when it moves it from one place to another. There's no such thing as a "signed move" (to a location of the same size - there is a signed move for larger or smaller destinations). The CPU only cares about the representation when it does arithmetic on the byte. The CPU knows whether to do signed or unsigned arithmetic according to the op-code that you (or the compiler on

一、linux模块化机制简介 模块化的优势： linux内核是单内核结构，由于所有内容都集成在一起，效率很高，但可扩展性和可维护性相对较差，模块机制弥补这一缺陷。 Linux模块可以通过静态或动态的方法加载到内核空间，静 态加载是指 在内核启动过程中加载；动态加载是指在内核运行的过程中随时加载。一个模块被加载到内核中时，就成为内核代码的一部分。模块加载入系统时，系统修改内核中的符号表，将新加载的模块提供的资源和符号添加到内核符号表中，以便模块间的通信。 从代码的特征上来看，模块就是可以完成一个独立功能的一组函数的集合，但以特殊的方法来编译，从而使之可以在需要时随时安装，在不需要时随时卸载。它们扩展了操作系统内核功能却不需要重新编译内核、启动系统。 Linux 内核模块主要由以下几个部分组成： 模块加载函数（必须）：当通过insmod命令加载内核模块时，模块的加载函数会自动被内核执行，完成本模块相关初始化工作； 模块卸载函数（必须）：当通过rmmod命令卸载模块时，模块的卸载函数会自动被内核执行，完成与模块加载函数相反的功能； 模块许可证声明（必须）：模块许可证（LICENCE）声明描述内核模块的许可权限，如果不声明LICENCE,模块被加载时将收到内核被污染的警告。大多数 模块参数（可选）：模块参数是模块被加载的时候可以被传递给他的值，它本身对应模块内部的全局变量； 模块导出符号

I have seen these mentioned in the context of C and C++, but what is the difference between signed and unsigned variables? coobird Signed variables , such as signed integers will allow you to represent numbers both in the positive and negative ranges . Unsigned variables , such as unsigned integers, will only allow you to represent numbers in the positive . Unsigned and signed variables of the same type (such as int and byte ) both have the same range (range of 65,536 and 256 numbers, respectively), but unsigned can represent a larger magnitude number than the corresponding signed variable .

写在前面：通过uboot的阅读我学到了很多东西，高手写的代码就是不一样。 代码阅读顺序： 1.第一阶段（Stage 1） 第一阶段的启动代码在 cpu\<cpu type>\start.s中，完成的工作主要有： CPU自身初始化：包括 MMU，Cache，时钟系统，SDRAM 控制器等的初始化 重定位：把自己从非易失性存储器搬移到 RAM中 分配堆栈空间，设置堆栈指针 清零 BSS 数据段 跳转到第二阶段入口函数 start_armboot() /Uboot114/u-boot-1.1.4/cpu/arm926ejs/start.S 2.第二阶段（Stage 2） 第二阶段是 u-boot 的主体，入口点是 lib_arm\board.c 中的 start_armboot()函数，完成的主要工作包括： 为 U-boot 内部私有数据分配存储空间，并清零 依次调用函数指针数组 init_sequence 中定义的函数进行一系列的初始化 如果系统支持 NOR Flash，调用 flash_init ()和 display_flash_config ()初始化并显示检测到的器件信息（AT91SAM9260EK不需要） 如果系统支持LCD或VFD，调用lcd_setmem()或vfd_setmem()计算帧缓冲(Framebuffer)大小，然后在 BSS 数据段之后为

上一篇文章写的是linux下通过gcc完成程序源文件的编译执行的过程。以及makefile文件的编写，最后在终端平台输出myhello word！ 有了这个基础，这次学习的就是通过linux编译生成的代码在ARM上完成硬件实现。因为还不涉及到系统移植，所以还是裸板程序开发。 1.源代码编写 ARM裸板程序需要代码原料主要包括：汇编文件，C文件，makefile文件。每个文件都有各自功能。 （1）汇编文件 完成关看门狗；配置时钟；初始化sdram；设置栈；以及跳转到C函数执行入口（相当于main函数），代码如下（该例程不需要配置时钟和sdram）。 @****************************************************************************** @ File：crt0.S @ 功能：通过它转入C程序 @****************************************************************************** @注：正常汇编程序还需要初始化时钟，SDRAM功能，但对于点亮LED不需要。直接使用12Mhz .text .global _start _start: @程序代码段开始处，各段在链接脚本定义 ldr r0,=0x53000000 @看门狗控制寄存器地址

Please take a look at this simple program: #include <iostream> #include <vector> using namespace std; int main() { vector<int> a; std::cout << "vector size " << a.size() << std::endl; int b = -1; if (b < a.size()) std::cout << "Less"; else std::cout << "Greater"; return 0; } I'm confused by the fact that it outputs "Greater" despite it's obvious that -1 is less than 0. I understand that size method returns unsigned value but comparison is still applied to -1 and 0. So what's going on? can anyone explain this? Because the size of a vector is an unsigned integral type. You are comparing an

调试中打印管脚可以用SWO管脚代替PB3脚 keil配置如下 1.在新建工程里面加入 #include <stdio.h> #define ITM_Port8(n) (*((volatile unsigned char *)(0xE0000000+4*n))) #define ITM_Port16(n) (*((volatile unsigned short*)(0xE0000000+4*n))) #define ITM_Port32(n) (*((volatile unsigned long *)(0xE0000000+4*n))) #define DEMCR (*((volatile unsigned long *)(0xE000EDFC))) #define TRCENA 0x01000000 struct __FILE { int handle; /* Add whatever you need here */ }; FILE __stdout; FILE __stdin; int fputc(int ch, FILE *f) { if (DEMCR & TRCENA) { while (ITM_Port32(0) == 0); ITM_Port8(0) = ch; } return(ch); } 2.配置软件 其中core频率是根据单片机频率来设置，必须一样 如上设置完后