isqrt32i.c

msp430F437三相电表DEMO(编译器 IAR 3.42A）

//--------------------------------------------------------------------------
//
//  Software for MSP430 based e-meters.
//
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//
//  File: isqrt32i.c
//
//  Steve Underwood <[e-mail]>
//  Texas Instruments Hong Kong Ltd.
//
//  $Id: isqrt32i.c,v 1.2 2003/07/28 10:15:41 XHKJAMES Exp $
//
//--------------------------------------------------------------------------
#include <stdint.h>
#include "emeter-toolkit-custom.h"
#include "emeter-toolkit.h"

int16_t isqrt32i(register int32_t h)
{
    register int32_t x;
    register int32_t y;
    register int16_t i;

    //The body of this routine only calculates the square
    //root of numbers up to 30-bit. It blows up if x exceeds
    //0x3FFFFFFF, so we protect against this at the
    //beginning. It makes no real difference to the results,
    //since even the square root of 0x3FFF0001 hits the
    //maximum positive integer.
    if (h > 0x3FFF0001)
        return 0x7FFF;
    //The answer is calculated as a 32 bit value, where the last
    //16 bits are fractional. It is then half bit rounded to a
    //16 bit integer.
#if defined(__GNUC__)  &&  defined(__MSP430__)
    x = 0x80000000;
    y = 0;
    i = 32;
    __asm__ (
        "1: \n"
        " setc \n"
        " rlc   %A[x] \n"
        " rlc   %B[x] \n"
        " sub   %A[x],%A[y] \n"
        " subc  %B[x],%B[y] \n"
        " jhs   2f \n"
        " add   %A[x],%A[y] \n"
        " addc  %B[x],%B[y] \n"
        " sub   #2,%A[x] \n"
        "2: \n"
        " inc   %A[x] \n"
        " rla   %A[h] \n"
        " rlc   %B[h] \n"
        " rlc   %A[y] \n"
        " rlc   %B[y] \n"
        " rla   %A[h] \n"
        " rlc   %B[h] \n"
        " rlc   %A[x] \n"
        " rlc   %B[x] \n"
        " dec   %[i] \n"
        " jne   1b \n"
        : [x] "+r"(x), [y] "+r"(y)
        : [h] "r"(h), [i] "r"(i));
#elif defined(__AQCOMPILER__)
    x =
    y = 0;
    i = 32;
    /$
sqrt10i
        setc
        rlc     @x.1
        rlc     @x.0
        sub     @x.1,@y.1
        subc    @x.0,@y.0
        jhs     sqrt12i
        add     @x.1,@y.1
        addc    @x.0,@y.0
        sub     #2,@x.1
sqrt12i
        inc     @x.1
        rla     @h.1
        rlc     @h.0
        rlc     @y.1
        rlc     @y.0
        rla     @h.1
        rlc     @h.0
        rlc     @y.1
        rlc     @y.0
        dec     @i
        jne     sqrt10i
    $/
#else
    x =
    y = 0;
    for (i = 0;  i < 32;  i++)
    {
        x = (x << 1) | 1;
        if (y < x)
            x -= 2;
        else
            y -= x;
        x++;
        y <<= 1;
        if ((h & 0x80000000))
            y |= 1;
        h <<= 1;
        y <<= 1;
        if ((h & 0x80000000))
            y |= 1;
        h <<= 1;
    }
#endif
    //x now contains the answer, with a fractional point
    //between bits 15 and 16. Now we do half bit rouding,
    //and return an integer result.
    return  ((x + 0x8000L) >> 16);
}