China DOS Union

In the Quake3 engine, there is such a "mars algorithm":

// 

// Calculate the reciprocal of the square root of parameter x 

// 

float InvSqrt (float x) 

{ 

float xhalf = 0.5f*x; 

int i = *(int*)&x; 

i = 0x5f3759df - (i >> 1); // Calculate the first approximate root 

x = *(float*)&i; 

x = x*(1.5f - xhalf*x*x); // Newton's iteration method 

return x; 

} 

Personally, I think that set /a supports bit operations, and it should be possible to implement the reciprocal of the square root.

```
In the SET command, two new command-line switches are added:

SET /A expression
SET /P variable=

The /A command-line switch specifies that the string to the right of the equal sign is a numerical expression to be evaluated. This expression evaluator is simple and supports the following operations in decreasing order of precedence:

() - Grouping
! ~ - - Unary operators
* / % - Arithmetic operators
+ - - Arithmetic operators
<< >> - Logical shifts
- Bitwise "AND"
^ - Bitwise "XOR"
| - Bitwise "OR"
= *= /= %= += -= - Assignment
&= ^= |= <<= >>=
, - Expression separator
```
　　Microsoft's explanations have always been vague. Except for being able to use arithmetic operators and assignment symbols proficiently, I have never understood the rest. Please explain if anyone has used it.

　　In CMD, you can't directly calculate decimal multiplication; you still have to operate bit by bit. If you can understand how the set /a symbols are used, the problem of square roots is estimated to be solved easily.

Square root can be solved using Pascal's triangle

Using set /a is too cumbersome, and division is anyway cumbersome

[ Last edited by he200377 on 2006-10-16 at 00:34 ]