Down below is my current code so far, including all the specific instructions, but as it includes work I have completed, I'll summarize here:
Rules:
1. max constant we can use is 0xff
2. the only operations we can use are: ! ~ & ^ | + << >>
so no subtraction
also, sometimes some of the operations are banned for certain functions
3. Can't make or call any functions
4. Can't use any control constructs (if, do, while, for, switch, etc.) or non-specified operations (&&, ||, -, ?)
5. No casting of any kind
Assumptions:
1. My machine is 32-bit and uses 2s complements
2. Right shifts are arithmetic
Things I'm having special trouble with:
1. logicalShift
Spoiler:
Can't think of anything on this
2. bitCount
Spoiler:
The only thing I could think of here would be to keep shifting it to the right, adding the final bit each time, but sadly for loops are disallowed.
3. Bang
Spoiler:
Honestly I'm not entirely sure what the bang does. We haven't gone over it in class at all and google hasn't been very helpful. I do know that if you say something like !( x == y ) it would mean x is not equal to y, but logical operators are pretty much all kicked out (no == allowed).
4. leastBitPos
Spoiler:
Now I actually found a solution here, but my teacher said it's invalid since I used a negative mark...
5. addOK
Spoiler:
The problem with this is basically the right logical shift that I need to do, so once that goes tumbling down this one will be simple.
There are more at the bottom that I haven't got yet, but I haven't started on them yet. I'm going to continue working on them, but any help you could give would be greatly appreciated!
- Code: Select all
You will provide your solution to the Data Lab by
editing the collection of functions in this source file.
CODING RULES:
Replace the "return" statement in each function with one
or more lines of C code that implements the function. Your code
must conform to the following style:
int Funct(arg1, arg2, ...) {
/* brief description of how your implementation works */
int var1 = Expr1;
...
int varM = ExprM;
varJ = ExprJ;
...
varN = ExprN;
return ExprR;
}
Each "Expr" is an expression using ONLY the following:
1. Integer constants 0 through 255 (0xFF), inclusive. You are
not allowed to use big constants such as 0xffffffff.
2. Function arguments and local variables (no global variables).
3. Unary integer operations ! ~
4. Binary integer operations & ^ | + << >>
Some of the problems restrict the set of allowed operators even further.
Each "Expr" may consist of multiple operators. You are not restricted to
one operator per line.
You are expressly forbidden to:
1. Use any control constructs such as if, do, while, for, switch, etc.
2. Define or use any macros.
3. Define any additional functions in this file.
4. Call any functions.
5. Use any other operations, such as &&, ||, -, or ?:
6. Use any form of casting.
You may assume that your machine:
1. Uses 2s complement, 32-bit representations of integers.
2. Performs right shifts arithmetically.
3. Has unpredictable behavior when shifting an integer by more
than the word size.
EXAMPLES OF ACCEPTABLE CODING STYLE:
/*
* pow2plus1 - returns 2^x + 1, where 0 <= x <= 31
*/
int pow2plus1(int x) {
/* exploit ability of shifts to compute powers of 2 */
return (1 << x) + 1;
}
/*
* pow2plus4 - returns 2^x + 4, where 0 <= x <= 31
*/
int pow2plus4(int x) {
/* exploit ability of shifts to compute powers of 2 */
int result = (1 << x);
result += 4;
return result;
}
NOTES:
1. Use the dlc (data lab checker) compiler (described in the handout) to
check the legality of your solutions.
2. Each function has a maximum number of operators (! ~ & ^ | + << >>)
that you are allowed to use for your implementation of the function.
The max operator count is checked by dlc. Note that '=' is not
counted; you may use as many of these as you want without penalty.
3. Use the btest test harness to check your functions for correctness.
4. The maximum number of ops for each function is given in the
header comment for each function. If there are any inconsistencies
between the maximum ops in the writeup and in this file, consider
this file the authoritative source.
}
#endif
/*
* STEP 3: Modify the following functions according the coding rules.
*
* IMPORTANT. TO AVOID GRADING SURPRISES:
* 1. Use the dlc compiler to check that your solutions conform
* to the coding rules.
* 2. Use the btest test harness to check that your solutions produce
* the correct answers. Watch out for corner cases around Tmin and Tmax.
*/
/*
* bitNor - ~(x|y) using only ~ and &
* Example: bitNor(0x6, 0x5) = 0xFFFFFFF8
* Legal ops: ~ &
* Max ops: 8
* Rating: 1
*/
int
bitNor(int x, int y) {
return (~x)&(~y);
}
/*
* bitXor - x^y using only ~ and &
* Example: bitXor(4, 5) = 1
* Legal ops: ~ &
* Max ops: 14
* Rating: 2
*/
int
bitXor(int x, int y) {
int a = x&(~y);
int b = (~x)&y;
return ~((~a)&(~b));
}
/*
* isNotEqual - return 0 if x == y, and 1 otherwise
* Examples: isNotEqual(5,5) = 0, isNotEqual(4,5) = 1
* Max ops: 6
* Rating: 2
*/
int
isNotEqual(int x, int y) {
return !(x == y); // Invalid
}
/*
* getByte - Extract byte n from word x
* Bytes numbered from 0 (LSB) to 3 (MSB)
* Examples: getByte(0x12345678,1) = 0x56
* Legal ops: ! ~ & ^ | + << >>
* Max ops: 6
* Rating: 2
*/
int
getByte(int x, int n) {
return (x>>(n<<3))&0xff;
}
/*
* copyLSB - set all bits of result to least significant bit of x
* Example: copyLSB(5) = 0xFFFFFFFF, copyLSB(6) = 0x00000000
* Legal ops: ! ~ & ^ | + << >>
* Max ops: 5
* Rating: 2
*/
int
copyLSB(int x) {
return(x << 31) >> 31;
}
/*
* logicalShift - shift x to the right by n, using a logical shift
* Can assume that 1 <= n <= 31
* Examples: logicalShift(0x87654321,4) = 0x08765432
* Legal ops: ~ & ^ | + << >>
* Max ops: 16
* Rating: 3
*/
int
logicalShift(int x, int n) {
return (x << n);
}
/*
* bitCount - returns count of number of 1's in word
* Examples: bitCount(5) = 2, bitCount(7) = 3
* Legal ops: ! ~ & ^ | + << >>
* Max ops: 40
* Rating: 4
*/
int
bitCount(int x) {
return 2;
}
/*
* bang - Compute !x without using !
* Examples: bang(3) = 0, bang(0) = 1
* Legal ops: ~ & ^ | + << >>
* Max ops: 12
* Rating: 4
*/
int
bang(int x) {
return 2;
}
/*
* leastBitPos - return a mask that marks the position of the
* least significant 1 bit. If x == 0, return 0
* Example: leastBitPos(96) = 0x20
* Legal ops: ! ~ & ^ | + << >>
* Max ops: 6
* Rating: 4
*/
int
leastBitPos(int x) {
return x&(-x);
}
/*
* TMax - return maximum two's complement integer
* Legal ops: ! ~ & ^ | + << >>
* Max ops: 4
* Rating: 1
*/
int
tmax(void) {
return 2147483647;
}
/*
* isNonNegative - return 1 if x >= 0, return 0 otherwise
* Example: isNonNegative(-1) = 0. isNonNegative(0) = 1.
* Legal ops: ! ~ & ^ | + << >>
* Max ops: 6
* Rating: 3
*/
int
isNonNegative(int x) {
return 2;
}
/*
* isGreater - if x > y then return 1, else return 0
* Example: isGreater(4,5) = 0, isGreater(5,4) = 1
* Legal ops: ! ~ & ^ | + << >>
* Max ops: 24
* Rating: 3
*/
int
isGreater(int x, int y) {
return 2;
}
/*
* divpwr2 - Compute x/(2^n), for 0 <= n <= 30
* Round toward zero
* Examples: divpwr2(15,1) = 7, divpwr2(-33,4) = -2
* Legal ops: ! ~ & ^ | + << >>
* Max ops: 15
* Rating: 2
*/
int
divpwr2(int x, int n) {
return 2;
}
/*
* absVal - absolute value of x (except returns TMin for TMin)
* Example: absVal(-1) = 1.
* Legal ops: ! ~ & ^ | + << >>
* Max ops: 10
* Rating: 4
*/
int
absVal(int x) {
return 2;
}
/*
* addOK - Determine if can compute x+y without overflow
* Example: addOK(0x80000000,0x80000000) = 0,
* addOK(0x80000000,0x70000000) = 1,
* Legal ops: ! ~ & ^ | + << >>
* Max ops: 20
* Rating: 3
*/
int
addOK(int x, int y) {
int b = x >> 31;
int c = y >> 31;
int d = (b>>(0<<31))&0xffffffff;
int e = (c>>(0<<31))&0xffffffff;
int a = (d + e) >> 1;
return !(a == 1); // WHY THIS NO WORK!?
}
