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如何将一个结构与两个无符号的short视为一个无符号的int?(C)

fixed-point struct c

snakile · 技术社区 · 14 年前

我创建了一个表示定点正数的结构。我希望小数点两边的数字由2个字节组成。

typedef struct Fixed_t {
    unsigned short floor; //left side of the decimal point
    unsigned short fraction; //right side of the decimal point
} Fixed;

现在我想加上两个定点数, Fixed x 和 Fixed y . 为了做到这一点,我将它们视为整数并相加。

(Fixed) ( (int)x + (int)y );

但正如我的Visual Studio 2010编译器所说,我无法在 Fixed 和 int .

正确的方法是什么?

编辑:我没有承诺 {short floor, short fraction} 执行固定。

9 回复 | 直到 14 年前

R.. GitHub STOP HELPING ICE 14 年前

typedef union Fixed {
    uint16_t w[2];
    uint32_t d;
} Fixed;
#define Floor w[((Fixed){1}).d==1]
#define Fraction w[((Fixed){1}).d!=1]

short int
Floor Fraction floor() foo.Floor foo.Fraction

uint16_t w[2]; uint32_t d;

(Fixed){1} (Fixed){{1,0}} {1,0} ((Fixed){1}).d ((Fixed){1}).d==1 ((Fixed){1}).d!=1

w[1] w[0]

Steve Jessop 14 年前

floor fraction

short

unsigned int val = (x.floor << 16) + x.fraction;

Fixed int

unsigned int result = (((uint64_t)x) * y) >> 16

unsigned int val;
assert(sizeof(Fixed) == sizeof(unsigned int))              // could be a static test
assert(2 * sizeof(unsigned short) == sizeof(unsigned int)) // could be a static test
memcpy(&val, &x, sizeof(unsigned int));

CashCow 14 年前

typedef struct Fixed_t {
   union { 
        struct { unsigned short floor; unsigned short fraction }; 
        unsigned int whole;
         };
} Fixed;

Fred Foo 14 年前

Fixed int Fixed add(Fixed a, Fixed b)

Mark Elliot 14 年前

FRAC_MAX

 // c = a + b
 void fixed_add( Fixed* a, Fixed* b, Fixed* c){
     unsigned short carry = 0;
     if((int)(a->floor) + (int)(b->floor) > FRAC_MAX){
         carry = 1;
         c->fraction = a->floor + b->floor - FRAC_MAX; 
     }
     c->floor = a->floor + b->floor + carry;
 }

void fixed_add( Fixed* a, Fixed *b, Fixed *c){
    int ia = a->floor << 16 + a->fraction;
    int ib = b->floor << 16 + b->fraction;
    int ic = ia + ib;
    c->floor = ic >> 16;
    c->fraction = ic - c->floor;
}

Bernd 14 年前

typedef union {
    struct Fixed_t {
        unsigned short floor; //left side of the decimal point
        unsigned short fraction; //right side of the decimal point
    } Fixed;
    int Fixed_int;
}

Benoit Thiery 14 年前

-1

Andy 14 年前

// add two Fixed 
Fixed operator+( Fixed a, Fixed b ) 
{   
...
}

//add Fixed and int
Fixed operator+( Fixed a, int b ) 
{   
...
}

-1

Vovanium 14 年前

*(newtype *)&var