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387 rindas
13 KiB
387 rindas
13 KiB
/*
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* CS:APP Data Lab
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*
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* <Please put your name and userid here>
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*
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* bits.c - Source file with your solutions to the Lab.
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* This is the file you will hand in to your instructor.
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*
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* WARNING: Do not include the <stdio.h> header; it confuses the dlc
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* compiler. You can still use printf for debugging without including
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* <stdio.h>, although you might get a compiler warning. In general,
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* it's not good practice to ignore compiler warnings, but in this
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* case it's OK.
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*/
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#if 0
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/*
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* Instructions to Students:
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*
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* STEP 1: Read the following instructions carefully.
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*/
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You will provide your solution to the Data Lab by
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editing the collection of functions in this source file.
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INTEGER CODING RULES:
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Replace the "return" statement in each function with one
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or more lines of C code that implements the function. Your code
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must conform to the following style:
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int Funct(arg1, arg2, ...) {
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/* brief description of how your implementation works */
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int var1 = Expr1;
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...
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int varM = ExprM;
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varJ = ExprJ;
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...
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varN = ExprN;
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return ExprR;
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}
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Each "Expr" is an expression using ONLY the following:
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1. Integer constants 0 through 255 (0xFF), inclusive. You are
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not allowed to use big constants such as 0xffffffff.
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2. Function arguments and local variables (no global variables).
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3. Unary integer operations ! ~
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4. Binary integer operations & ^ | + << >>
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Some of the problems restrict the set of allowed operators even further.
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Each "Expr" may consist of multiple operators. You are not restricted to
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one operator per line.
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You are expressly forbidden to:
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1. Use any control constructs such as if, do, while, for, switch, etc.
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2. Define or use any macros.
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3. Define any additional functions in this file.
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4. Call any functions.
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5. Use any other operations, such as &&, ||, -, or ?:
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6. Use any form of casting.
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7. Use any data type other than int. This implies that you
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cannot use arrays, structs, or unions.
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You may assume that your machine:
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1. Uses 2s complement, 32-bit representations of integers.
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2. Performs right shifts arithmetically.
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3. Has unpredictable behavior when shifting if the shift amount
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is less than 0 or greater than 31.
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EXAMPLES OF ACCEPTABLE CODING STYLE:
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/*
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* pow2plus1 - returns 2^x + 1, where 0 <= x <= 31
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*/
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int pow2plus1(int x) {
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/* exploit ability of shifts to compute powers of 2 */
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return (1 << x) + 1;
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}
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/*
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* pow2plus4 - returns 2^x + 4, where 0 <= x <= 31
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*/
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int pow2plus4(int x) {
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/* exploit ability of shifts to compute powers of 2 */
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int result = (1 << x);
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result += 4;
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return result;
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}
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FLOATING POINT CODING RULES
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For the problems that require you to implement floating-point operations,
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the coding rules are less strict. You are allowed to use looping and
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conditional control. You are allowed to use both ints and unsigneds.
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You can use arbitrary integer and unsigned constants. You can use any arithmetic,
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logical, or comparison operations on int or unsigned data.
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You are expressly forbidden to:
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1. Define or use any macros.
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2. Define any additional functions in this file.
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3. Call any functions.
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4. Use any form of casting.
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5. Use any data type other than int or unsigned. This means that you
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cannot use arrays, structs, or unions.
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6. Use any floating point data types, operations, or constants.
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NOTES:
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1. Use the dlc (data lab checker) compiler (described in the handout) to
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check the legality of your solutions.
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2. Each function has a maximum number of operations (integer, logical,
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or comparison) that you are allowed to use for your implementation
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of the function. The max operator count is checked by dlc.
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Note that assignment ('=') is not counted; you may use as many of
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these as you want without penalty.
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3. Use the btest test harness to check your functions for correctness.
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4. Use the BDD checker to formally verify your functions
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5. The maximum number of ops for each function is given in the
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header comment for each function. If there are any inconsistencies
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between the maximum ops in the writeup and in this file, consider
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this file the authoritative source.
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/*
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* STEP 2: Modify the following functions according the coding rules.
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*
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* IMPORTANT. TO AVOID GRADING SURPRISES:
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* 1. Use the dlc compiler to check that your solutions conform
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* to the coding rules.
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* 2. Use the BDD checker to formally verify that your solutions produce
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* the correct answers.
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*/
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#endif
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/* Copyright (C) 1991-2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* This header is separate from features.h so that the compiler can
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include it implicitly at the start of every compilation. It must
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not itself include <features.h> or any other header that includes
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<features.h> because the implicit include comes before any feature
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test macros that may be defined in a source file before it first
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explicitly includes a system header. GCC knows the name of this
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header in order to preinclude it. */
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/* glibc's intent is to support the IEC 559 math functionality, real
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and complex. If the GCC (4.9 and later) predefined macros
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specifying compiler intent are available, use them to determine
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whether the overall intent is to support these features; otherwise,
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presume an older compiler has intent to support these features and
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define these macros by default. */
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/* wchar_t uses Unicode 10.0.0. Version 10.0 of the Unicode Standard is
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synchronized with ISO/IEC 10646:2017, fifth edition, plus
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the following additions from Amendment 1 to the fifth edition:
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- 56 emoji characters
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- 285 hentaigana
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- 3 additional Zanabazar Square characters */
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//1
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/*
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* bitXor - x^y using only ~ and &
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* Example: bitXor(4, 5) = 1
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* Legal ops: ~ &
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* Max ops: 14
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* Rating: 1
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*/
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int bitXor(int x, int y) {
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return ~(~x&~y)&~(x&y);
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}
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/*
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* tmin - return minimum two's complement integer
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* Legal ops: ! ~ & ^ | + << >>
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* Max ops: 4
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* Rating: 1
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*/
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int tmin(void) {
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return 0x1<<31;
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}
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//2
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/*
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* isTmax - returns 1 if x is the maximum, two's complement number,
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* and 0 otherwise
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* Legal ops: ! ~ & ^ | +
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* Max ops: 10
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* Rating: 1
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*/
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int isTmax(int x) {
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int y = (0x7f<<24)+(0xff<<16)+(0xff<<8)+0xff;
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x = x^y;
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return !x;
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}
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/*
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* allOddBits - return 1 if all odd-numbered bits in word set to 1
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* where bits are numbered from 0 (least significant) to 31 (most significant)
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* Examples allOddBits(0xFFFFFFFD) = 0, allOddBits(0xAAAAAAAA) = 1
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* Legal ops: ! ~ & ^ | + << >>
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* Max ops: 12
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* Rating: 2
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*/
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int allOddBits(int x) {
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int a = (0xaa<<24)+(0xaa<<16)+(0xaa<<8)+0xaa
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;
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return !((a&x)^a);
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}
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/*
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* negate - return -x
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* Example: negate(1) = -1.
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* Legal ops: ! ~ & ^ | + << >>
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* Max ops: 5
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* Rating: 2
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*/
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int negate(int x) {
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return ~x+1;
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}
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//3
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/*
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* isAsciiDigit - return 1 if 0x30 <= x <= 0x39 (ASCII codes for characters '0' to '9')
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* Example: isAsciiDigit(0x35) = 1.
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* isAsciiDigit(0x3a) = 0.
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* isAsciiDigit(0x05) = 0.
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* Legal ops: ! ~ & ^ | + << >>
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* Max ops: 15
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* Rating: 3
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*/
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int isAsciiDigit(int x) {
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//下边界为加够了就溢出，比这个大
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//上边界为加不够就不溢出
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int downstream = ~0x30+1;
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int upstream = ~0x3a+1;
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int leftside = !((downstream+x)>>31); //超过0x30就符号变为0
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int rightside = !!((upstream+x)>>31); //小于0x39就符号仍然为1
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return leftside&rightside;
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}
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/*
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* conditional - same as x ? y : z
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* Example: conditional(2,4,5) = 4
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* Legal ops: ! ~ & ^ | + << >>
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* Max ops: 16
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* Rating: 3
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*/
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int conditional(int x, int y, int z) {
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x = !!(x);
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x = ~x+1;
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return (x&y)|(~x&z);
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}
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/*
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* isLessOrEqual - if x <= y then return 1, else return 0
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* Example: isLessOrEqual(4,5) = 1.
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* Legal ops: ! ~ & ^ | + << >>
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* Max ops: 24
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* Rating: 3
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*/
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int isLessOrEqual(int x, int y) {
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int tmp = ~y+1;
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tmp = tmp+x-1;
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tmp = tmp >> 31;//如果比y大，则为0，比y小等于，为1
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return !!tmp;
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}
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//4
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/*
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* logicalNeg - implement the ! operator, using all of
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* the legal operators except !
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* Examples: logicalNeg(3) = 0, logicalNeg(0) = 1
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* Legal ops: ~ & ^ | + << >>
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* Max ops: 12
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* Rating: 4
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*/
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int logicalNeg(int x) {
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return ((x|(~x+1))>>31)+1;
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}
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/* howManyBits - return the minimum number of bits required to represent x in
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* two's complement
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* Examples: howManyBits(12) = 5
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* howManyBits(298) = 10
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* howManyBits(-5) = 4
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* howManyBits(0) = 1
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* howManyBits(-1) = 1
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* howManyBits(0x80000000) = 32
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* Legal ops: ! ~ & ^ | + << >>
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* Max ops: 90
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* Rating: 4
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*/
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int howManyBits(int x) {
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x = ((~(x>>31))&x)|(x>>31&~x);//左边为如果为正数，则保留；右边为如果为负数，则取反
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//先从最大开始查找
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int tf = !!(x>>16); //如果小于等于16位，则为0，否则为1
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int b16 = tf << 4; //长度超过16位，记录值b16为16，否则为0，代表至少16位
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x = x>>b16; //右移动b16位，超过16位则探讨16位以上的，少于16位则探讨16位以下的
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tf = !!(x>>8); //开始探讨剩余部位是否超过8位,超过看超过多少，没超过看余下多少
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int b8 = tf << 3;//长度超过8位，记录值b8为8，否则为0，代表再多至少8位
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x = x>>b8;
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tf = !!(x>>4);
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int b4 = tf << 2 ; //8找4,长度超过4位，记录值b4为4，否则为0，代表再多至少4位
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x = x>>b4;
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tf = !!(x>>2);
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int b2 = tf << 1; //4找2,长度超过2位，记录值b2为2，否则为0，代表再多至少2位
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x = x>>b2;
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tf = !!(x>>1); //2找1，长度超过1位，记录值b1为1，否则为0，代表再多至少1位
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int b1 = tf << 0;
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x = x>>b1;
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int b0 = x;//截断到只剩单个数字,这个数字是1就再多一位,是0就不会增加
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return b0+b1+b2+b4+b8+b16+1; //正数多一位补码最高位，负数因为取反未+1，理应再加1，故两个输出表达式一致
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}
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//float
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/*
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* floatScale2 - Return bit-level equivalent of expression 2*f for
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* floating point argument f.
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* Both the argument and result are passed as unsigned int's, but
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* they are to be interpreted as the bit-level representation of
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* single-precision floating point values.
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* When argument is NaN, return argument
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* Legal ops: Any integer/unsigned operations incl. ||, &&. also if, while
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* Max ops: 30
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* Rating: 4
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*/
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unsigned floatScale2(unsigned uf) {
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unsigned sign = (0x80<<24)&uf;
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unsigned exp = ((0x7f<<24)+(0x80<<16))&uf;
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unsigned frac = ((0x7f<<16)+(0xff<<8)+0xff)&uf;
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if(exp == ((0x7f<<24)+(0x80<<16)))
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return uf; //如果是exp全为255,frac全是0就是无穷，不是就是NaN，都直接return
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if(exp == 0x0){
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if(frac == 0x0)
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return uf; //exp全为0,frac全为0，则为0，0*2=0，原样不动
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return (frac<<1)|sign|exp;//exp全为0,frac不全为0，注意到非规格化极小和规格化之间是连续的，即frac第一位为1时，左移会把exp变为非全0，回到规格化
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}
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return (exp+(0x80<<16))|sign|frac;
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}
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/*
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* floatFloat2Int - Return bit-level equivalent of expression (int) f
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* for floating point argument f.
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* Argument is passed as unsigned int, but
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* it is to be interpreted as the bit-level representation of a
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* single-precision floating point value.
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* Anything out of range (including NaN and infinity) should return
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* 0x80000000u.
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* Legal ops: Any integer/unsigned operations incl. ||, &&. also if, while
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* Max ops: 30
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* Rating: 4
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*/
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int floatFloat2Int(unsigned uf) {
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unsigned sign = ((0x80<<24)&uf)>>31;
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unsigned exp = (((0x7f<<24)+(0x80<<16))&uf)>>23;
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unsigned frac = ((0x7f<<16)+(0xff<<8)+0xff)&uf;
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unsigned base = (frac+(0x80<<16));//加1后的基底（对于常规数）
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unsigned notpermit = 0x80 << 24; //不满足题干要求时应输出的数值
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int bias = (exp-127)-23;//真实需要左移的
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if(sign==0)
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sign = 1;
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else
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sign = -1;
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if(exp == 255)
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return notpermit;//足够大
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if(exp == 0)
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return 0;//足够小
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if(bias <=0){
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if(bias<=-24)
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bias = -24;
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return sign*(base>>(-bias));
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}
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else{
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if(bias>=9)
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return notpermit;
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return sign*(base<<bias);
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}
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}
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// #include "floatPower2.c"
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