hermite.c

著名的 helix realplayer 基于手机 symbian 系统的 播放器全套源代码

	f = s->step_f;
	for (i = 0; i < 4; i++) {
		inframes += outframes * (f & 0xff);		/* add 24x8 partial product */
		inframes = (inframes + 0xff) >> 8;		/* shift, rounding up */
		f >>= 8;
	}
	/* integer part */
	inframes += outframes * s->step_i;

	return (int)(inframes * s->nchans);

    /* equivalent method using __int64 
	 * 
	 * step64 = ((__int64)s->step_i << 32) + (__int64)s->step_f;
	 * inframes = ( (__int64)outframes * step64);
	 * inframes += (__int64)(0x00000000ffffffff);		COMMENT: (add 1.0 - 2^-32 to 32.32 number)
	 * return (int)((inframes >> 32) * s->nchans);
	 */

    /* equivalent method using double-precision floats
	 * 
	 * double step;
	 * outframes = (s->nchans == 2 ? outsamps >> 1 : outsamps);
	 * step = s->step_i + (s->step_f / 4294967296.0);
	 * inframes = (int) ceil((double)outframes * step);
	 * return (inframes * s->nchans);
	 */

    /* equivalent method using an empty (null) resample 
	 * 
	 * outframes = (s->nchans == 2 ? outsamps >> 1 : outsamps);
	 * for (i = f = currOut = 0; currOut < outframes; currOut++) {
	 * 	f += s->step_f;
	 * 	i += s->step_i + (f < s->step_f);	COMMENT: add with carry 
	 * }
	 * if (f)		COMMENT: ceiling (if any fractional part, round up) 
	 * 	i++;
	 * return (int)(i * s->nchans);
	 */
}

/* Get number of frames of delay in the Hermite resampler
 * 
 * Parameters
 * ----------
 * void *inst              instance pointer 
 * 
 * return value            frames of delay
 *
 * Notes
 * -----
 * - always two frames of delay (2 samples per channel)
 */
int
RAGetDelayHermite(void *inst)
{
	return 2;
}

/* Cubic Hermite interpolation - one channel
 * 
 * Parameters
 * ----------
 * void *inbuf             pointer to buffer of input data (16-bit PCM)
 * int insamps             number of samples in inbuf
 * cvtFunctionType cvt     conversion function pointer, ignored
 * short *outbuf           output buffer, must be large enough to hold RAGetMaxOutputHermite(insamps) samples
 * void *inst              instance pointer 
 * 
 * return value            number of output samples generated and placed in outbuf, -1 if error
 *
 * Notes
 * -----
 * - no restrictions on number of insamps
 * - inbuf MUST contain 16-bit PCM data, the cvt function is ignored
 */
int
RAResampleMonoHermite(void *inbuf, int insamps, tConverter *pCvt, short *outbuf, int outstride, void *inst)
{
	STATE *s = (STATE *)inst;
	UINT f, step_i, step_f;
	int outsamps, i, acc0;
	int x0, x1, x2, x3, frac;
	short *inptr;

	/* restore state */
	i = s->time_i;
	f = s->time_f;
	step_i = s->step_i;
	step_f = s->step_f;
	outsamps = 0;
	inptr = (short *)inbuf;

	if (s->nchans != 1 || outstride != 1)
		return -1;

	/* mono */
	while (i < insamps) {
		
		if (i < 3) {
			x3 = (i < 3 ? s->hist[i+0] : inptr[i-3]) << 12;
			x2 = (i < 2 ? s->hist[i+1] : inptr[i-2]) << 12;
			x1 = (i < 1 ? s->hist[i+2] : inptr[i-1]) << 12;
		} else {
			x3 = inptr[i-3] << 12;
			x2 = inptr[i-2] << 12;
			x1 = inptr[i-1] << 12;
		}
		x0 = inptr[i] << 12;
		frac = f >> 1;

		/* 4-tap Hermite, using Farrow structure */
		acc0 = (3 * (x2 - x1) + x0 - x3) >> 1;
		acc0 = MulShift31(acc0, frac);
		acc0 += 2 * x1 + x3 - ((5 * x2 + x0) >> 1);
		acc0 = MulShift31(acc0, frac);
		acc0 += (x1 - x3) >> 1;
		acc0 = MulShift31(acc0, frac);
		acc0 += x2;

		f += step_f;
		i += step_i + (f < step_f);	/* add with carry */

		acc0 = (acc0 + (1<<11)) >> 12;
		if (acc0 > +32767) acc0 = +32767;
		if (acc0 < -32768) acc0 = -32768;
		outbuf[outsamps++] = (short)acc0;
	}

	/* save delay samples for next time (hist[0] = oldest, hist[2] = newest) */
	s->hist[0] = (insamps < 3 ? s->hist[insamps+0] : inptr[insamps-3]);
	s->hist[1] = (insamps < 2 ? s->hist[insamps+1] : inptr[insamps-2]);
	s->hist[2] = (insamps < 1 ? s->hist[insamps+2] : inptr[insamps-1]);

	/* save state */
	s->time_f = f;
	s->time_i = i - insamps;

	return outsamps;
}

/* Cubic Hermite interpolation - two channels
 * 
 * Parameters
 * ----------
 * void *inbuf             pointer to buffer of input data (16-bit PCM, interleaved LRLRLR...)
 * int insamps             number of samples in inbuf
 * cvtFunctionType cvt     conversion function pointer, ignored
 * short *outbuf           output buffer, must be large enough to hold RAGetMaxOutputHermite(insamps) samples
 * void *inst              instance pointer 
 * 
 * return value            number of output samples generated and placed in outbuf, -1 if error
 *
 * Notes
 * -----
 * - no restrictions on number of insamps
 * - inbuf MUST contain 16-bit PCM data, the cvt function is ignored
 * - insamps must be even, function will exit with error if not
 */
int
RAResampleStereoHermite(void *inbuf, int insamps, tConverter *pCvt, short *outbuf, int outstride, void *inst)
{
	STATE *s = (STATE *)inst;
	UINT f, step_i, step_f;
	int outsamps, i, acc0, acc1, j;
	int x0, x1, x2, x3, frac;
	short *inptr;

	/* restore state */
	i = s->time_i;
	f = s->time_f;
	step_i = s->step_i;
	step_f = s->step_f;
	outsamps = 0;
	inptr = (short *)inbuf;

	/* fail if odd number of input samples */
	if (s->nchans != 2 || insamps & 0x01 || outstride != 2)
		return -1;

	/* stereo - assume insamps is even */
	insamps /= 2;				/* number of stereo frames - consume samples two at a time */
	while (i < insamps) {
		frac = f >> 1;
		j = 2*i;

		/* left */
		if (i < 3) {
			x3 = (i < 3 ? s->hist[j+0] : inptr[j-6]) << 12;
			x2 = (i < 2 ? s->hist[j+2] : inptr[j-4]) << 12;
			x1 = (i < 1 ? s->hist[j+4] : inptr[j-2]) << 12;
		} else {
			x3 = inptr[j-6] << 12;
			x2 = inptr[j-4] << 12;
			x1 = inptr[j-2] << 12;
		}
		x0 = inptr[j] << 12;

		/* 4-tap Hermite, using Farrow structure */
		acc0 = (3 * (x2 - x1) + x0 - x3) >> 1;
		acc0 = MulShift31(acc0, frac);
		acc0 += 2 * x1 + x3 - ((5 * x2 + x0) >> 1);
		acc0 = MulShift31(acc0, frac);
		acc0 += (x1 - x3) >> 1;
		acc0 = MulShift31(acc0, frac);
		acc0 += x2;

		/* right */
		if (i < 3) {
			x3 = (i < 3 ? s->hist[j+1] : inptr[j-5]) << 12;
			x2 = (i < 2 ? s->hist[j+3] : inptr[j-3]) << 12;
			x1 = (i < 1 ? s->hist[j+5] : inptr[j-1]) << 12;
		} else {
			x3 = inptr[j-5] << 12;
			x2 = inptr[j-3] << 12;
			x1 = inptr[j-1] << 12;
		}
		x0 = inptr[j+1] << 12;

		/* 4-tap Hermite, using Farrow structure */
		acc1 = (3 * (x2 - x1) + x0 - x3) >> 1;
		acc1 = MulShift31(acc1, frac);
		acc1 += 2 * x1 + x3 - ((5 * x2 + x0) >> 1);
		acc1 = MulShift31(acc1, frac);
		acc1 += (x1 - x3) >> 1;
		acc1 = MulShift31(acc1, frac);
		acc1 += x2;

		f += step_f;
		i += step_i + (f < step_f);	/* add with carry */

		acc0 = (acc0 + (1<<11)) >> 12;
		if (acc0 > +32767) acc0 = +32767;
		if (acc0 < -32768) acc0 = -32768;
		outbuf[outsamps++] = (short)acc0;

		acc1 = (acc1 + (1<<11)) >> 12;
		if (acc1 > +32767) acc1 = +32767;
		if (acc1 < -32768) acc1 = -32768;
		outbuf[outsamps++] = (short)acc1;
	}

	/* save delay samples for next time (hist[0] = oldest left, hist[1] = oldest right, ...) */
	s->hist[0] = (insamps < 3 ? s->hist[2*(insamps+0) + 0] : inptr[2*(insamps-3) + 0]);
	s->hist[2] = (insamps < 2 ? s->hist[2*(insamps+1) + 0] : inptr[2*(insamps-2) + 0]);
	s->hist[4] = (insamps < 1 ? s->hist[2*(insamps+2) + 0] : inptr[2*(insamps-1) + 0]);

	s->hist[1] = (insamps < 3 ? s->hist[2*(insamps+0) + 1] : inptr[2*(insamps-3) + 1]);
	s->hist[3] = (insamps < 2 ? s->hist[2*(insamps+1) + 1] : inptr[2*(insamps-2) + 1]);
	s->hist[5] = (insamps < 1 ? s->hist[2*(insamps+2) + 1] : inptr[2*(insamps-1) + 1]);

	/* save state */
	s->time_f = f;
	s->time_i = i - insamps;

	return outsamps;
}