# ➢ 算法导论笔记 - 排序和顺序统计量

• 待排序的项称为 记录（record），每个记录包含一个 关键字（key），即排序问题中要重排的值，记录的剩余部分由 卫星数据（statellite data）组成。
• 如果输入数组中仅有常数个元素需要在排序过程中存储在数组之外，则称排序算法是 原址的（in place）。插入排序可以在$\Theta(n^2)$时间内将n个数排好序，是一种非常快的原址排序算法；归并排序有更好的渐近运行时间$\Theta(n\lg n)$，但它使用的MERGE过程并不是原址的。

# 算法基础

## 插入排序

//INSERTION-SORT(A)
for j = 2 to A.length
key = A[j]
//Insert A[j] into the sorted sequence A[1..j-1]
i = j - 1
while i > 0 and A[i] > key
A[i + 1] = A[i]
i = i - 1
A[i+1] = key

• 循环不变式：初始化、保持、终止

##分析算法

• 单处理器计算模型：随机访问机（random-access machine，RAM）：算数指令、数据移动指令、控制指令。
• 最坏情况、平均情况、增长量级

# ➢ Computer Organization and Design 笔记 - Multicores, Multiprocessors, and Clusters

## Introduction

multiprocessor

A computer system with at least two processors. This is in contrast to a uniprocessor , which has one.

job-level parallelism or process-level parallelism

Utilizing multiple processors by running independent programs simultaneously.

parallel processing program

A single program that runs on multiple processors simultaneously.

cluster

A set of compters connected over a local area network (LAN) that functions as a single large message-passing multiprocessor.

multicore microprocessor

A microprocessor containing multiple processors (“cores”) in a single integrated circuit.

# ➢ Computer Organization and Design 笔记 - Storage and Other I/O Topics

## Dependability, Reliability, and Availability

Dependability is the quality of delivered service such that reliance can justifiably be placed on this service.

Reliability is a measure of the continuous service accomplishment(or, equivalently, of the time to failure) from a reference point.

mean time to failure(MTTF) is a reliability measure. annual failure rate(AFR) is the percentage of devices that would be expected to fail in a year for a given MTTF. Service interruption is measured as mean time to repair(MTTR). Mean time between failures(MTBF) is simply the sum of MTTF and MTTR.

Availability is a measure of service accomplishment with respect to the alternation between the two states of accomplishment and interruption.

Availability = MTTF / MTBF

3 ways to improve MTTF:

1. Fault avoidance: preventing fault occurrence by construction.
2. Fault tolerance: using redundancy to allow the service to comply with the service specification despite faults occurring, which applies primarily to hardware faults.
3. Fault forecasting: predicting the presence and creation of faults, which applies to hardware and software faults, allowing the component to be replaced before it fails.

# ➢ Computer Organization and Design 笔记 - Exploiting Memory Hierarchy

## Introduction

Principle of locality

• Temporal locality : If a data location is referenced then it will tend to be referenced again soon.
• spatial locality : If a data location is referenced, data locations with nearby addresses will tend to be referenced soon.

Memory hierarchy

A structrue that uses multiple levels of memories; as the distance from the processor increases, the size of the memories and the access time both increase.

The main memory is implemented from DRAM, levels closer to the processor use SRAM, the largest and slowest level is usually magnetic disk.

# ➢ Computer Organization and Design 笔记 - The Processor

## Introduction

A abstract view of the implementation of the MIPS subset showing the major functional units and the major connections between them:

The basic implementation of the MIPS subset, including the necessary multiplexors and control lines:

asserted

The signal is logically high or true.

deasserted

The signal is logically low or false.

Clocking methodology

The approach used to determine when data is valid and stable relative to the clock.

Edge-triggered clocking

A clocking scheme in which all state changes occur on a clock edge.

control signal

A signal used for multiplexor selection or for directing the operation of a functional unit; contrasts with a data signal , which contains information that is operated on by a funcional unit.

The state element is changed only when the write control signal is asserted and a clock edge occurs.

# ➢ Computer Organization and Design 笔记 - Arithmetic for Computers

1. Add (add), and immediate (addi), and subtract (sub) cause exceptions on overflow. MIPS detects overflow with an exception (or interrupt ), which is an unscheduled procedure call. The address of current instruction is saved and the computer jumps to predefined address to invoke the appropriate routine for that exception.

MIPS uses exception program counter (EPC) to contain the address of the instruction that causes the exception. The instruction move from system control (mfc0) is used to copy EPC into a general-purpose register.

2. Add unsigned (addu), add immediate unsigned (addiu), and subtract unsigned (subu) do not cause exceptions on overflow. Programmers can trap overflow anyway: when overflow occurs, the sign bit of the result is not properly set. Compairing with sign bits of operands, the sign bit of the result can be determined.

SIMD (single instruction, multiple data): By partitioning the carry chains within a 64-bit adder, a processor could perform simultaneous operations on a short vecters of eight 8-bit operands, four 16-bit operands, etc. Vectors and 8-bit data often appears in multimedia routine.

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