Computer Systems: A Programmer's Perspective (3rd Edition)
3rd Edition
ISBN: 9780134092997
Author: Bryant
Publisher: PEARSON
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Chapter 2, Problem 2.71HW
You just started working for a company that is implementing a set of procedures to operate on a data structure where 4 signed bytes are packed into a 32-bit unsigned. Bytes within the word are numbered from 0 (least significant) to 3
(most significant). You have been assigned the task of implementing a function for a machine using two’s-complement arithmetic and arithmetic right shifts with the following prototype:
/* Declaration of data type where 4 bytes are packed
into an unsigned */
typedef unsigned packed_t;
/* Extract byte from word. Return as signed integer */
int xbyte (packed_t word, int bytenum);
That is, the function will extract the designated byte and sign extend it to be a 32-bit int.
Your predecessor (who was fired for incompetence) wrote the following code:
/* Failed attempt at xbyte */
int xbyte (packed_t word, int bytenum)
{
return (word >>(bytenum <<3)) & 0xFF;
}
- A. What is wrong with this code?
- B. Give a correct implementation of the function that uses only left and right shifts, along with one subtraction.
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BELOW MCQ GIVEN ANSWER CAN BE MORE THAN ONE OPTION. PLEASE PROVIDE CORRECT ANSWERS.
-------------------
Q3 :- The ANSI C function below causes the program in which it runs to malfunction . Which of the following connection will help to perform function successfully ?
/* Return a count of all the bits set in bytes */
int bitcount (unsigned char c)
{
unsigned char x , b , count =0;
for (b = 0 , x= 1 ; !(x & 0x100); ++b, x <<=1) {
if (x | c )
++count;
}
return count;
}
A) change the type of x to a type larger than unsigned char.
B) remove the extraneous variable b.
C) change the return type to unsigned char .
D) change if ( x | c) to if ( x & c) inside the for loop.
E) change ! (c & 0x100) to ( x < 0x100) inside the for loop.
Suppose we number the bytes in a w-bit word from 0 (least significant) to w/8 – 1 (most significant). Write code for the following C function, which will return an unsigned value in which byte i of argument x has been replaced by byte b:
unsigned replace_byte (unsigned x, int i, unsigned char b);
Here are some examples showing how the function should work:
replace_byte(0x12345678, 2, 0xAB) --> 0x12AB5678
replace_byte(0x12345678, 0, 0xAB) --> 0x123456AB
Bit-Level Integer Coding Rules
In several of the following problems, we will artificially restrict what programming constructs you can use to help you gain a better understanding of the bit-level, logic, and arithmetic operations of C. In answering these problems, your code must follow these rules:
Allowed operations
All bit-level and logic operations.
Left and right shifts, but only with shift amounts between 0 and w – 1.
Addition and subtraction.
Equality (==) and inequality (!=) tests. (Some of the problems do not allow…
Write a function to convert a string, such as: "-13.232e-5" into a double-precision floatingpoint number. The address of the string should be passed in register $a0. The function shouldreturn the double-precision floating-point number in $f0. Conversion should terminate if theend of the string is reached (NULL byte), or an invalid character is encountered, such as aspace, comma,
Chapter 2 Solutions
Computer Systems: A Programmer's Perspective (3rd Edition)
Ch. 2.1 - Practice Problem 2.1 (solution page 143) Perform...Ch. 2.1 - Prob. 2.2PPCh. 2.1 - Prob. 2.3PPCh. 2.1 - Practice Problem 2.4 (solution page 144) Without...Ch. 2.1 - Prob. 2.5PPCh. 2.1 - Prob. 2.6PPCh. 2.1 - Prob. 2.7PPCh. 2.1 - Prob. 2.8PPCh. 2.1 - Practice Problem 2.9 solution page 146 Computers...Ch. 2.1 - Prob. 2.10PP
Ch. 2.1 - Prob. 2.11PPCh. 2.1 - Prob. 2.12PPCh. 2.1 - Prob. 2.13PPCh. 2.1 - Prob. 2.14PPCh. 2.1 - Prob. 2.15PPCh. 2.1 - Prob. 2.16PPCh. 2.2 - Prob. 2.17PPCh. 2.2 - Practice Problem 2.18 (solution page 149) In...Ch. 2.2 - Prob. 2.19PPCh. 2.2 - Prob. 2.20PPCh. 2.2 - Prob. 2.21PPCh. 2.2 - Prob. 2.22PPCh. 2.2 - Prob. 2.23PPCh. 2.2 - Prob. 2.24PPCh. 2.2 - Prob. 2.25PPCh. 2.2 - Practice Problem 2.26 (solution page 151) You are...Ch. 2.3 - Prob. 2.27PPCh. 2.3 - Prob. 2.28PPCh. 2.3 - Prob. 2.29PPCh. 2.3 - Practice Problem 2.30 (solution page 153) Write a...Ch. 2.3 - Prob. 2.31PPCh. 2.3 - Practice Problem 2.32 (solution page 153) You are...Ch. 2.3 - Prob. 2.33PPCh. 2.3 - Prob. 2.34PPCh. 2.3 - Practice Problem 2.35 (solution page 154) You are...Ch. 2.3 - Prob. 2.36PPCh. 2.3 - Practice Problem 2.37 solution page 155 You are...Ch. 2.3 - Prob. 2.38PPCh. 2.3 - Prob. 2.39PPCh. 2.3 - Practice Problem 2.40 (solution page 156) For each...Ch. 2.3 - Prob. 2.41PPCh. 2.3 - Practice Problem 2.42 (solution page 156) Write a...Ch. 2.3 - Practice Problem 2.43 (solution page 157) In the...Ch. 2.3 - Prob. 2.44PPCh. 2.4 - Prob. 2.45PPCh. 2.4 - Prob. 2.46PPCh. 2.4 - Prob. 2.47PPCh. 2.4 - Prob. 2.48PPCh. 2.4 - Prob. 2.49PPCh. 2.4 - Prob. 2.50PPCh. 2.4 - Prob. 2.51PPCh. 2.4 - Prob. 2.52PPCh. 2.4 - Practice Problem 2.53 (solution page 160) Fill in...Ch. 2.4 - Practice Problem 2.54 (solution page 160) Assume...Ch. 2 - Compile and run the sample code that uses...Ch. 2 - Try running the code for show_bytes for different...Ch. 2 - Prob. 2.57HWCh. 2 - Write a procedure is_little_endian that will...Ch. 2 - Prob. 2.59HWCh. 2 - Prob. 2.60HWCh. 2 - Prob. 2.61HWCh. 2 - Write a function int_shifts_are_arithmetic() that...Ch. 2 - Fill in code for the following C functions....Ch. 2 - Write code to implement the following function: /...Ch. 2 - Write code to implement the following function: /...Ch. 2 - Write code to implement the following function: / ...Ch. 2 - You are given the task of writing a procedure...Ch. 2 - Prob. 2.68HWCh. 2 - Write code for a function with the following...Ch. 2 - Write code for the function with the following...Ch. 2 - You just started working for a company that is...Ch. 2 - You are given the task of writing a function that...Ch. 2 - Write code for a function with the following...Ch. 2 - Write a function with the following prototype: /...Ch. 2 - Prob. 2.75HWCh. 2 - The library function calloc has the following...Ch. 2 - Prob. 2.77HWCh. 2 - Write code for a function with the following...Ch. 2 - Prob. 2.79HWCh. 2 - Write code for a function threefourths that, for...Ch. 2 - Prob. 2.81HWCh. 2 - Prob. 2.82HWCh. 2 - Prob. 2.83HWCh. 2 - Prob. 2.84HWCh. 2 - Prob. 2.85HWCh. 2 - Intel-compatible processors also support an...Ch. 2 - Prob. 2.87HWCh. 2 - Prob. 2.88HWCh. 2 - We are running programs on a machine where values...Ch. 2 - You have been assigned the task of writing a C...Ch. 2 - Prob. 2.91HWCh. 2 - Prob. 2.92HWCh. 2 - following the bit-level floating-point coding...Ch. 2 - Following the bit-level floating-point coding...Ch. 2 - Following the bit-level floating-point coding...Ch. 2 - Following the bit-level floating-point coding...Ch. 2 - Prob. 2.97HW
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