1/13/05
Due: Assigned: 1/25/05
CprE 211 Spring 2005 Homework 1 Solution
Last Name First Name Section
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Remember, these homework exercises not only give you practice with course concepts, but also represent the types of questions you will be tested on in an exam.
1
Assigned: 1/13/05
Due: 1/25/05
1.
Digital Logic Number Representation [14]
Consider each of the following data items, and fill in the blanks. a. Character `a' (ASCII character code) = ___0x61_________ Hex (8-bit) b. Character `A' (ASCII character code) = _____01000001_______ Binary (8-bit) c. Character `1' (ASCII character code) = _______0x31_____ Hex (8-bit) d. Character `1'(ASCII character code) = _______49_____ Decimal e. Integer 23 = ________17____ Hex (8-bit) f. 32-bit Unsigned Integer Range = _______0_____ - ___4,294,967,295____ Decimal g. 32-bit Unsigned Integer Range = _____0_______ - _____FFFFFFFF___ Hex h. 32-bit Signed 2's Complement Integer Range = ______-2147483648___ - ______2147483647_ Decimal i. (Unsigned) 0xA23C + 0x1EF0 = _____0xC12C____ Hex j. (Unsigned) 0xA23C - 0x1EF0 = _______0x834C___ Hex k. (Signed 2's Complement) 0xA23C - 0x1EF0 = __0x834C_____ Hex l. 368 Decimal = _____0x170___ Hex (16-bit) m. Logical shift right, 4 times, of 368 Decimal = ______23____ Decimal (16-bit) n. Bitwise AND of 368 Decimal with 231 Decimal = ____96_____ Decimal (16-bit)
2
Assigned: 1/13/05
Due: 1/25/05
2. Bitwise Operations [4] Complete the following: a. if (byVal & 0xC3) What does this statement test for? Check if any bits of 0,1,6 or 7 of byVal is 1 b. if (~byVal & 0xC3) What does this statement test for? Check if any bits of 0,1,6 or 7 of byVal is 0 c. if ((byVal & 0xC3) == 0x81) What does this statement test for? Check if byVal is equal to 10xxxx01, x can be 0 and 1 d. if ((byVal & 0xC0) && (byVal & 0x03)) What does this statement test for? Check if at least one of bits 6 and 7 AND at least one of bits 0 and 1 is 1 3. Consider the C code fragments and questions in d. and e., and fill in the blanks [6]. a. [1] short byKey, Row, Col; ... byKey = 0x1C; ... Row = byKey & 0x07; Col = (byKey & 0x38) >> 3; What is the value of Row (stated as a decimal number): _________4_
What is the value of Col (stated as a decimal number): _________3_
3
Assigned: 1/13/05
Due: 1/25/05
b. [1] char byInput; ... if ( ( byInput & 0x01 ) || ( byInput & 0x20 ) ) If byInput = 0x64, is the condition TRUE or FALSE? __TRUE____________ (Recall that || is logical OR.)
c. [2] Using if-else statements in C, write a code fragment that implements the following behavior: If either bit 2 or 5 of byVal (a char variable) is equal to 1, then call function Increase_Threshold(); or if bit 3 = 1 and bit 4 = 0, call function Decrease_Threshold(); otherwise call function Book_Keeping(). if(byVal&0x24) {Increase_Threshold();} else if((byVal&0x08)&&!(byVal&0x10)) {Decrease_Threshold();} else {Book_Keeping();}
d. [2] Using bit-level and shift and logical operations and for loop statement, write a C program to count the number of 1's in variable x of "unsigned short" type. unsigned short x; int count=0; for(int i=0; i<=15; i++) { if(x&0x01) { count++; } x>>1; }
4
Assigned: 1/13/05
Due: 1/25/05
4.
C Programming [4]
a. [1] Write a C expression that will yield a word consisting of the odd bits of x, and the even bits of y. For operands x = 0x21212121 and y = 0x12121212, this would give 0x03030303. Assume a word is four bytes. (x&0x55555555)|(y&0xAAAAAAAA)
b. [1] Given the following function prototype in C, answer i. iv. below: unsigned char Read_Results (char * pResults, char byArray[], int pos); i. ii. What is the size in bytes of the return value of the function? _____1 byte____ What is the size in bytes of each of the parameters passed to the function? ____width of memory_____ char *pResults ____width of memory____ char byArray[] ____vary___ int pos (No credits for these questions are taken off if you are wrong. You can consider they are all 4 bytes here) iii. Write a C statement that reads the data at address (pResults+pos) and assigns it to the element of byArray at position pos. ByArray[0]=*(pResult+pos) iv. Write a C statement that clears bit 7 of the data at address (pResults+pos). *(pResult+pos)&0x7F c. [2] You just started working for a company that is implementing a set of procedures to operate on a data structure where four signed bytes are packed into a 32-bit unsigned. Bytes within the word are numbered from 0 (least significant) to 3 (most significant).
5
Assigned: 1/13/05
Due: 1/25/05
You have been assigned the task of implementing a function for a machine using two'scomplement 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; /* Write a new value into a dataword */ dataward replace_byte (packed_t dataword, int bytenum, char byteval);
That is, the function will replace the designated byte with a new value in byteval and return the result. The original dataword is unchanged. packet_t replace_byte(packet_t dataword, int bytenum, char byteVal) { packet_t temp=dataword&(~(0xFF<<(bytenum*8))); return(temp|(byteVal<<(bytenum*8))); }
5. Embedded Programming [3] a. Rank the following languages in order of their "level of abstraction" for the programmer, where 1 is the lowest level of abstraction. Hint: what does abstraction mean? _2____ Assembly language _1____ Machine language _4____ Object-oriented high-level language (e.g., C++, Java) _3____ High-level language (e.g., C, Pascal) _5____ Application-level language (e.g., Microsoft Excel macros) b. In embedded programming, how may abstraction help program design? Abstraction makes programming and debugging easy, it easy to manage the complexity of the problem. c. In embedded programming, how may abstraction hurt program implementation? It adds unnecessary low-level code and hurts performance (speed)
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