Verilog 加法器和减法器(6)
2024-10-18 18:22:59
为了减小行波进位加法器中进位传播延迟的影响,可以尝试在每一级中快速计算进位,如果能在较短时间完成计算,则可以提高加法器性能。
我们可以进行如下的推导:
设 gi=xi&yi, pi = xi +y i
ci+1 = xi&y i+x i&ci+yi&ci=xi&yi + (xi+yi)&ci=g i+pi&c i = gi+pi&(gi-1+pi-1&ci-1)=g i+pi&g i-1+pi&pi-1&ci-1= ….=gi+pi &gi-1+pi &pi-1&gi-2+…+pi&pi-1…p2&p1 &g0+pi &pi-1..p1 &p0&c0; 实现这个逻辑电路的加法器是超前进位加法器。从公式中,可以看出门延时要比行波进位加法器小很多。但是电路复杂,逻辑门的扇入数量将限制超前进位加法器的速度。
由于扇入数量限制,通常我们仅实现4位超前进位加法器和8位超前进位加法器,然后在串联成16/32/64等高位加法器。
下面是4位和8位的超前进位加法器代码:
module adder4_fast(
cin,
x,
y,
s,
cout
); input cin;
input [3:0] x;
input [3:0] y;
output [3:0] s;
output cout; wire [4:0] g,p,c; assign c[0] = cin;
assign p = x | y;
assign g = x & y;
//assign c[1] = g[0] | (p[0] & c[0]);
//assign c[2] = g[1] | (p[1] & (g[0] | (p[0] & c[0])));
//assign c[3] = g[2] | (p[2] & (g[1] | (p[1] & (g[0] | (p[0] & c[0])))));
//assign c[4] = g[3] | (p[3] & (g[2] | (p[2] & (g[1] | (p[1] & (g[0] | (p[0] & c[0])))))));
assign c[1] = g[0] | (p[0] & c[0]);
assign c[2] = g[1] | (p[1]&g[0])|(p[1]&p[0]&c[0]);
assign c[3] = g[2] | (p[2]&g[1])|(p[2]&p[1]&g[0])|(p[2]&p[1]&p[0]&c[0]);
assign c[4] = g[3] | (p[3]&g[2])|(p[3]&p[2]&g[1])|(p[3]&p[2]&p[1]&g[0])|(p[3]&p[2]&p[1]&p[0]&c[0]);
assign s = x^y^c[3:0];
assign cout = c[4]; endmodule
module adder8_fast(
cin,
x,
y,
s,
cout
); input cin;
input [7:0] x;
input [7:0] y;
output [7:0] s;
output cout; wire [8:0] g,p,c; assign c[0] = cin;
assign p = x | y;
assign g = x & y;
//assign c[1] = g[0] | (p[0] & c[0]);
//assign c[2] = g[1] | (p[1] & (g[0] | (p[0] & c[0])));
//assign c[3] = g[2] | (p[2] & (g[1] | (p[1] & (g[0] | (p[0] & c[0])))));
//assign c[4] = g[3] | (p[3] & (g[2] | (p[2] & (g[1] | (p[1] & (g[0] | (p[0] & c[0])))))));
//assign c[5] = g[4] | (p[4] & (g[3] | (p[3] & (g[2] | (p[2] & (g[1] | (p[1] & (g[0] | (p[0] & c[0])))))))));
//assign c[6] = g[5] | (p[5] & (g[4] | (p[4] & (g[3] | (p[3] & (g[2] | (p[2] & (g[1] | (p[1] & (g[0] | (p[0] & c[0])))))))))));
//assign c[7] = g[6] | (p[6] & (g[5] | (p[5] & (g[4] | (p[4] & (g[3] | (p[3] & (g[2] | (p[2] & (g[1] | (p[1] & (g[0] | (p[0] & c[0])))))))))))));
//assign c[8] = g[7] | (p[7] & (g[6] | (p[6] & (g[5] | (p[5] & (g[4] | (p[4] & (g[3] | (p[3] & (g[2] | (p[2] & (g[1] | (p[1] & (g[0] | (p[0] & c[0])))))))))))))));
assign c[1] = g[0] | (p[0] & c[0]);
assign c[2] = g[1] | (p[1]&g[0])|(p[1]&p[0]&c[0]);
assign c[3] = g[2] | (p[2]&g[1])|(p[2]&p[1]&g[0])|(p[2]&p[1]&p[0]&c[0]);
assign c[4] = g[3] | (p[3]&g[2])|(p[3]&p[2]&g[1])|(p[3]&p[2]&p[1]&g[0])|(p[3]&p[2]&p[1]&p[0]&c[0]);
assign c[5] = g[4] | (p[4]&g[3])|(p[4]&p[3]&g[2])|(p[4]&p[3]&p[2]&g[1])|(p[4]&p[3]&p[2]&p[1]&g[0])|(p[4]&p[3]&p[2]&p[1]&p[0]&c[0]);
assign c[6] = g[5] | (p[5]&g[4])|(p[5]&p[4]&g[3])|(p[5]&p[4]&p[3]&g[2])|(p[5]&p[4]&p[3]&p[2]&g[1])|(p[5]&p[4]&p[3]&p[2]&p[1]&g[0])|(p[5]&p[4]&p[3]&p[2]&p[1]&p[0]&c[0]);
assign c[7] = g[6] | (p[6]&g[5])|(p[6]&p[5]&g[4])|(p[6]&p[5]&p[4]&g[3])|(p[6]&p[5]&p[4]&p[3]&g[2])|(p[6]&p[5]&p[4]&p[3]&p[2]&g[1])|(p[6]&p[5]&p[4]&p[3]&p[2]&p[1]&g[0])|(p[6]&p[5]&p[4]&p[3]&p[2]&p[1]&p[0]&c[0]);
assign c[8] = g[7] | (p[7]&g[6])|(p[7]&p[6]&g[5])|(p[7]&p[6]&p[5]&g[4])|(p[7]&p[6]&p[5]&p[4]&g[3])|(p[7]&p[6]&p[5]&p[4]&p[3]&g[2])|(p[7]&p[6]&p[5]&p[4]&p[3]&p[2]&g[1])|(p[7]&p[6]&p[5]&p[4]&p[3]&p[2]&p[1]&g[0])|(p[7]&p[6]&p[5]&p[4]&p[3]&p[2]&p[1]&p[0]&c[0]);
assign s = x^y^c[7:0];
assign cout = c[8]; endmodule
下面的代码把4个超前进位加法器串联起来,形成一个32位加法器。
module addern_fast(
cin,
x,
y,
s,
cout
); input cin;
input [31:0] x;
input [31:0] y;
output [31:0] s;
output cout;
wire [2:0] cout_tmp; adder8_fast adder8_fast_0(.cin(cin),.x(x[7:0]),.y(y[7:0]),.s(s[7:0]),.cout(cout_tmp[0]));
adder8_fast adder8_fast_1(.cin(cout_tmp[0]),.x(x[15:8]),.y(y[15:8]),.s(s[15:8]),.cout(cout_tmp[1]));
adder8_fast adder8_fast_2(.cin(cout_tmp[1]),.x(x[23:16]),.y(y[23:16]),.s(s[23:16]),.cout(cout_tmp[2]));
adder8_fast adder8_fast_3(.cin(cout_tmp[2]),.x(x[31:24]),.y(y[31:24]),.s(s[31:24]),.cout(cout)); endmodule
下面是4位超前进位加法器的逻辑图:
8位超前进位加法器的波形结果。
最新文章
- 综合使用spring cloud技术实现微服务应用
- APP的缓存文件到底应该存在哪?看完这篇文章你应该就自己清楚了
- Python学习_列表推导和Lambda表达式
- c语言中static的语义
- 兼容PHP和Java的des加密解密代码分享
- 可用版本的host
- linux-2.6.33移植到FL2440
- Dapper入门教程(三)——Dapper Query查询
- kill 和killall----杀死进程
- 对Java配置文件中敏感信息进行加解密的工具类
- Android为TV端助力 EventBus出现has no public methods called onEvent的问题
- Ajax 请求请求 MVC WebAPI跨域问题;XMLHttpRequest cannot load
- shiro源码篇 - 疑问解答与系列总结,你值得拥有
- 快速幂的求解-java方法(int范围之内)
- fountion 的调用 和 打印返回值 + 占位符
- [NOI2016]区间 线段树
- SQL-重复记录查询的几种方法
- c++课程设计(日历)
- 给你的移动网站加点料:推荐下载App,如果本地安装则直接打开本地App(Android/IOS)
- VC++ IPv6的支持
热门文章
- SCTF2018-Event easiest web - phpmyadmin
- 清理.git文件
- [BZOJ3585]mex(莫队+分块)
- [POI2013]Polaryzacja
- Nginx简单总结
- [Java]struts2-spring整合时配置监听器
- 《Go语言实战》摘录:6.5 并发 - 通道
- Java深入 - 深入 Java自己定义注解
- react-router 从 v2/v3 to v4 迁移(翻译)
- 在vs2012下编译出现Msvcp120d.dll 丢失的问题