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7f23d71b6a
This function is useful for accumulating relative mouse motion if you want to only handle whole pixel movement.
e.g.
static float dx_frac, dy_frac;
float dx, dy;
/* Accumulate new motion with previous sub-pixel motion */
dx = event.motion.xrel + dx_frac;
dy = event.motion.yrel + dy_frac;
/* Split the integral and fractional motion, dx and dy will contain whole pixel deltas */
dx_frac = SDL_modff(dx, &dx);
dy_frac = SDL_modff(dy, &dy);
if (dx != 0.0f || dy != 0.0f) {
...
}
69 lines
1.7 KiB
C
69 lines
1.7 KiB
C
#include "SDL_internal.h"
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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/*
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* modf(double x, double *iptr)
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* return fraction part of x, and return x's integral part in *iptr.
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* Method:
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* Bit twiddling.
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*
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* Exception:
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* No exception.
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*/
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#include "math_libm.h"
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#include "math_private.h"
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static const double one = 1.0;
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double modf(double x, double *iptr)
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{
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int32_t i0,i1,_j0;
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u_int32_t i;
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EXTRACT_WORDS(i0,i1,x);
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_j0 = ((i0>>20)&0x7ff)-0x3ff; /* exponent of x */
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if(_j0<20) { /* integer part in high x */
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if(_j0<0) { /* |x|<1 */
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INSERT_WORDS(*iptr,i0&0x80000000,0); /* *iptr = +-0 */
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return x;
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} else {
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i = (0x000fffff)>>_j0;
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if(((i0&i)|i1)==0) { /* x is integral */
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*iptr = x;
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INSERT_WORDS(x,i0&0x80000000,0); /* return +-0 */
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return x;
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} else {
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INSERT_WORDS(*iptr,i0&(~i),0);
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return x - *iptr;
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}
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}
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} else if (_j0>51) { /* no fraction part */
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*iptr = x*one;
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/* We must handle NaNs separately. */
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if (_j0 == 0x400 && ((i0 & 0xfffff) | i1))
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return x*one;
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INSERT_WORDS(x,i0&0x80000000,0); /* return +-0 */
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return x;
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} else { /* fraction part in low x */
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i = ((u_int32_t)(0xffffffff))>>(_j0-20);
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if((i1&i)==0) { /* x is integral */
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*iptr = x;
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INSERT_WORDS(x,i0&0x80000000,0); /* return +-0 */
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return x;
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} else {
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INSERT_WORDS(*iptr,i0,i1&(~i));
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return x - *iptr;
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}
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}
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}
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libm_hidden_def(modf)
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