C.Interface.And.Implementations—bit vector的实现

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1、The  Bit  interface exports functions that manipulate bit vectors, which can be used to represent sets of integers from zero to  N− 1. For example, 256-bit vectors can be used to represent sets of characters efficiently.

2、Bit  provides most of the set-manipulation functions provided by  Set , and also a few functions that are specific to bit vectors. 

3、Unlike the sets provided by Set , the sets represented by bit vectors have a well-defined universe, which is the set of integers in the range zero to N− 1. Thus, Bit can provide functions that Set  cannot, such as the complement of a set.

本章bit vector类似于STL中的Bitsets，相当于一个很大的数组，数组的每一个元素是一位，每一位只存放1或者0。

由于都是0或者1，因此本章很多操作都是“&”“|”“^”等，由于之前这种代码很少写，正好趁此机会锻炼自己写运算代码的能力以及思维。

========================bit.h==================================

#ifndef BIT_INCLUDED
#define BIT_INCLUDED#define T Bit_T
typedef struct T *T;//exported functions
extern T    Bit_new   (int length);
extern int  Bit_length(T set);
extern int  Bit_count (T set);
extern void Bit_free  (T *set);
extern int  Bit_get   (T set, int n);
extern int  Bit_put   (T set, int n, int bit);
extern void Bit_clear (T set, int lo, int hi);
extern void Bit_set   (T set, int lo, int hi);
extern void Bit_not   (T set, int lo, int hi);
extern int  Bit_lt    (T s, T t);
extern int  Bit_eq    (T s, T t);
extern int  Bit_leq   (T s, T t);
extern void Bit_map   (T set,void apply(int n, int bit, void *cl), void *cl);
extern T    Bit_union (T s, T t);
extern T    Bit_inter (T s, T t);
extern T    Bit_minus (T s, T t);
extern T    Bit_diff  (T s, T t);#undef T
#endif

===================bit.c============================

#include <stdarg.h>
#include <string.h>
#include "assert.h"
#include "bit.h"
#include "mem.h"#define T Bit_Tstruct T{int length;unsigned char *bytes;unsigned long *words;
};//macros
#define BPW (8*sizeof(unsigned long))
#define nwords(len) ((((len)+BPW-1)&(~(BPW-1)))/BPW)
#define nbytes(len) ((((len)+8-1)&(~(8-1)))/8)
#define setop(sequal, snull, tnull, op)\if(s == t){ assert(s); return sequal; }\else if(s == NULL) { assert(t); return snull; }\else if(t == NULL) return tnull; \else{\int i; T set;\assert(s->length == t->length);\set = Bit_new(s->length);\for(i = nwords(s->length); --i >= 0; )\set->words[i] = s->words[i] op t->words[i];\return set;}//static data
unsigned char msbmask[] = {0xFF, 0xFE, 0xFC, 0xF8,0xF0, 0xE0, 0xC0, 0x80
};unsigned char lsbmask[] = {0x01, 0x03, 0x07, 0x0F,0x1F, 0x3F, 0x7F, 0xFF
};//static functions
static T copy(T t){T set;assert(t);set = Bit_new(t->length);if(t->length > 0)memcpy(set->bytes, t->bytes, nbytes(t->length));return set;
}//functions
T Bit_new(int length){T set;assert(length >= 0);NEW(set);if(length > 0)set->words = CALLOC(nwords(length),sizeof (unsigned long));elseset->words = NULL;set->bytes = (unsigned char *)set->words;set->length = length;return set;
}void Bit_free(T *set){assert(set && *set);FREE((*set)->words);FREE(*set);
}int Bit_length(T set){assert(set);return set->length;
}int Bit_count(T set){int length = 0, n;static char count[] = {0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4 };assert(set);for(n = nbytes(set->length); --n >= 0; ){unsigned char c = set->bytes[n];length += count[c&0xF] + count[c>>4];}return length;
}int Bit_get(T set, int n){assert(set);assert(0 <= n && n < set->length);return ((set->bytes[n/8]>>(n%8))&1);
}int Bit_put(T set, int n, int bit){int prev;assert(set);assert(bit == 0 || bit == 1);assert(0 <= n && n < set->length);prev = ((set->bytes[n/8]>>(n%8))&1);if(bit == 1)set->bytes[n/8] |= 1<<(n%8);elseset->bytes[n/8] &= ~(1 <<(n%8));return prev;
}void Bit_set(T set, int lo, int hi){//check set, lo, adn hiassert(set);assert(0 <= lo && hi < set->length);assert(lo <= hi);if(lo/8 < hi/8){//set the most significant bits in byte lo/8set->bytes[lo/8] |= msbmask[lo%8];//set all the bits in bytes lo/8+1..hi/8-1{int i;for(i = lo/8+1; i < hi/8; ++i)set->bytes[i] = 0xFF;}//set the least significant bits in byte in hi/8set->bytes[hi/8] |= lsbmask[hi%8];}else{//set bits lo%8..hi%8 in byte lo/8set->bytes[lo/8] |= (msbmask[lo%8]&lsbmask[hi%8]);}
}void Bit_clear(T set, int lo, int hi){//check set, lo, and hiassert(set);assert(0 < lo && hi < set->length);assert(lo <= hi);if(lo/8 < hi/8){int i;set->bytes[lo/8] &= ~msbmask[lo%8];for(i = lo/8 + 1; i < hi/8; ++i)set->bytes[i] = 0;set->bytes[hi/8] &= ~lsbmask[hi%8];}else{set->bytes[lo/8] &= ~(msbmask[lo%8]&lsbmask[hi%8]);}
}void Bit_not(T set, int lo, int hi){//check set, lo, and hiassert(set);assert(0 < lo && hi < set->length);assert(lo <= hi);if(lo/8 < hi/8){int i;set->bytes[lo/8] ^= msbmask[lo%8];for(i = lio/8 + 1; i < hi/8; ++i)set->bytes[i] ^= 0xFF;set->bytes[hi/8] ^= lsbmask[hi%8];}else{set->bytes[lo/8] ^= (msbmask[lo%8]&lsbmask[hi%8]);}
}void Bit_map(T set,void apply(int n, int bit, void *cl), void *cl){int n;assert(set);for(n = 0; n < set->length; ++n)apply(n, ((set->bytes[n/8]>>(n%8))&1), cl);
}int Bit_eq(T s, T t){int i;assert(s && t);assert(s->length == t->length);for(i = nwords(s->length); --i >= 0; )if(s->words[i] != t->words[i])return 0;return 1;
}int Bit_leq(T s, T t){int i;assert(s && t);assert(s->length == t->length);for(i = nwords(s->length); --i >= 0; )if((s->words[i] & ~t->words[i]) != 0)return 0;return 1;
}int Bit_lt(T s, T t){int i, lt = 0;assert(s && t);assert(s->length == t->length);for(i = nwords(s->length); --i >= 0; ){if((s->words[i]&~t->words[i]) != 0)return 0;else if(s->words[i] != t->words[i])lt |= 1;}return lt;
}T Bit_union(T s, T t){setop(copy(t), copy(t), copy(s), |);
}T Bit_inter(T s, T t){setop(copy(t),Bit_new(t->length), Bit_new(s->length), &);
}T Bit_minus(T s, T t){setop(Bit_new(s->length),Bit_new(t->length), copy(s), &~);
}T Bit_diff(T s, T t){setop(Bit_new(s->length), copy(t), copy(s), ^);
}

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