portapack-mayhem/firmware/baseband/dsp_decimate.cpp

/*
 * Copyright (C) 2014 Jared Boone, ShareBrained Technology, Inc.
 *
 * This file is part of PortaPack.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#include "dsp_decimate.hpp"

#include <hal.h>

namespace dsp {
namespace decimate {

buffer_c16_t TranslateByFSOver4AndDecimateBy2CIC3::execute(buffer_c8_t src, buffer_c16_t dst) {
	/* Translates incoming complex<int8_t> samples by -fs/4,
	 * decimates by two using a non-recursive third-order CIC filter.
	 */

	/* Derivation of algorithm:
	 * Original CIC filter (decimating by two):
	 * 	D_I0 = i3 * 1 + i2 * 3 + i1 * 3 + i0 * 1
	 * 	D_Q0 = q3 * 1 + q2 * 3 + q1 * 3 + q0 * 1
	 *
	 * 	D_I1 = i5 * 1 + i4 * 3 + i3 * 3 + i2 * 1
	 * 	D_Q1 = q5 * 1 + q4 * 3 + q3 * 3 + q2 * 1
	 *
	 * Translate -fs/4, phased 180 degrees, accomplished by complex multiplication
	 * of complex length-4 sequence:
	 *
	 * Substitute:
	 *	i0 = -i0, q0 = -q0
	 *	i1 = -q1, q1 =  i1
	 *	i2 =  i2, q2 =  q2
	 *	i3 =  q3, q3 = -i3
	 *	i4 = -i4, q4 = -q4
	 *	i5 = -q5, q5 =  i5
	 *
	 * Resulting taps (with decimation by 2, four samples in, two samples out):
	 *	D_I0 =  q3 * 1 +  i2 * 3 + -q1 * 3 + -i0 * 1
	 *	D_Q0 = -i3 * 1 +  q2 * 3 +  i1 * 3 + -q0 * 1
 	 *
	 *	D_I1 = -q5 * 1 + -i4 * 3 +  q3 * 3 +  i2 * 1
	 *	D_Q1 =  i5 * 1 + -q4 * 3 + -i3 * 3 +  q2 * 1
	 */

	// 6 cycles per complex input sample, not including loop overhead.
	uint32_t q1_i0 = _q1_i0;
	uint32_t q0_i1 = _q0_i1;
	/* 3:1 Scaled by 32 to normalize output to +/-32768-ish. */
	constexpr uint32_t scale_factor = 32;
	const uint32_t k_3_1 = 0x00030001 * scale_factor;
	uint32_t* src_p = reinterpret_cast<uint32_t*>(&src.p[0]);
	uint32_t* const src_end = reinterpret_cast<uint32_t*>(&src.p[src.count]);
	uint32_t* dst_p = reinterpret_cast<uint32_t*>(&dst.p[0]);
	while(src_p < src_end) {
		const uint32_t q3_i3_q2_i2 = *(src_p++);			// 3
		const uint32_t q5_i5_q4_i4 = *(src_p++);

		const uint32_t i2_i3 = __SXTB16(q3_i3_q2_i2, 16);			// 1: (q3_i3_q2_i2 ror 16)[23:16]:(q3_i3_q2_i2 ror 16)[7:0]
		const uint32_t q3_q2 = __SXTB16(q3_i3_q2_i2,  8);			// 1: (q3_i3_q2_i2 ror  8)[23:16]:(q3_i3_q2_i2 ror  8)[7:0]
		const uint32_t i2_q3 = __PKHTB(i2_i3, q3_q2, 16);			// 1: Rn[31:16]:(Rm>>16)[15:0]
		const uint32_t i3_q2 = __PKHBT(q3_q2, i2_i3, 16);			// 1:(Rm<<16)[31:16]:Rn[15:0]

		// D_I0 = 3 * (i2 - q1) + (q3 - i0)
		const uint32_t i2_m_q1_q3_m_i0 = __QSUB16(i2_q3, q1_i0);	// 1: Rn[31:16]-Rm[31:16]:Rn[15:0]-Rm[15:0]
		const uint32_t d_i0 = __SMUAD(k_3_1, i2_m_q1_q3_m_i0);		// 1: Rm[15:0]*Rs[15:0]+Rm[31:16]*Rs[31:16]

		// D_Q0 = 3 * (q2 + i1) - (i3 + q0)
		const uint32_t i3_p_q0_q2_p_i1 = __QADD16(i3_q2, q0_i1);	// 1: Rn[31:16]+Rm[31:16]:Rn[15:0]+Rm[15:0]
		const uint32_t d_q0 = __SMUSDX(i3_p_q0_q2_p_i1, k_3_1);		// 1: Rm[15:0]*Rs[31:16]–Rm[31:16]*RsX[15:0]
		const uint32_t d_q0_i0 = __PKHBT(d_i0, d_q0, 16);			// 1: (Rm<<16)[31:16]:Rn[15:0]

		const uint32_t i5_i4 = __SXTB16(q5_i5_q4_i4,  0);			// 1: (q5_i5_q4_i4 ror  0)[23:16]:(q5_i5_q4_i4 ror  0)[7:0]
		const uint32_t q4_q5 = __SXTB16(q5_i5_q4_i4, 24);			// 1: (q5_i5_q4_i4 ror 24)[23:16]:(q5_i5_q4_i4 ror 24)[7:0]
		const uint32_t q4_i5 = __PKHTB(q4_q5, i5_i4, 16);			// 1: Rn[31:16]:(Rm>>16)[15:0]
		const uint32_t q5_i4 = __PKHBT(i5_i4, q4_q5, 16);			// 1: (Rm<<16)[31:16]:Rn[15:0]

		// D_I1 = (i2 - q5) + 3 * (q3 - i4)
		const uint32_t i2_m_q5_q3_m_i4 = __QSUB16(i2_q3, q5_i4);	// 1: Rn[31:16]-Rm[31:16]:Rn[15:0]-Rm[15:0]
		const uint32_t d_i1 = __SMUADX(i2_m_q5_q3_m_i4, k_3_1);		// 1: Rm[15:0]*Rs[31:16]+Rm[31:16]*Rs[15:0]

		// D_Q1 = (i5 + q2) - 3 * (q4 + i3)
		const uint32_t q4_p_i3_i5_p_q2 = __QADD16(q4_i5, i3_q2);	// 1: Rn[31:16]+Rm[31:16]:Rn[15:0]+Rm[15:0]
		const uint32_t d_q1 = __SMUSD(k_3_1, q4_p_i3_i5_p_q2);		// 1: Rm[15:0]*Rs[15:0]–Rm[31:16]*Rs[31:16]
		const uint32_t d_q1_i1 = __PKHBT(d_i1, d_q1, 16);			// 1: (Rm<<16)[31:16]:Rn[15:0]
		*(dst_p++) = d_q0_i0;							// 3
		*(dst_p++) = d_q1_i1;

		q1_i0 = q5_i4;
		q0_i1 = q4_i5;
	}
	_q1_i0 = q1_i0;
	_q0_i1 = q0_i1;

	return { dst.p, src.count / 2, src.sampling_rate / 2 };
}

buffer_c16_t DecimateBy2CIC3::execute(
	buffer_c16_t src,
	buffer_c16_t dst
) {
	/* Complex non-recursive 3rd-order CIC filter (taps 1,3,3,1).
	 * Gain of 8.
	 * Consumes 16 bytes (4 s16:s16 samples) per loop iteration,
	 * Produces  8 bytes (2 s16:s16 samples) per loop iteration.
	 */
	uint32_t t1 = _iq0;
	uint32_t t2 = _iq1;
	uint32_t t3, t4;
	const uint32_t taps = 0x00000003;
	auto s = src.p;
	auto d = dst.p;
	const auto d_end = &dst.p[src.count / 2];
	uint32_t i, q;
	while(d < d_end) {
		i = __SXTH(t1, 0);			/* 1: I0 */
		q = __SXTH(t1, 16);			/* 1: Q0 */
		i = __SMLABB(t2, taps, i);	/* 1: I1*3 + I0 */
		q = __SMLATB(t2, taps, q);	/* 1: Q1*3 + Q0 */

		t3 = *__SIMD32(s)++;		/* 3: Q2:I2 */
		t4 = *__SIMD32(s)++;		/*    Q3:I3 */

		i = __SMLABB(t3, taps, i);	/* 1: I2*3 + I1*3 + I0 */
		q = __SMLATB(t3, taps, q);	/* 1: Q2*3 + Q1*3 + Q0 */
		int32_t si0 = __SXTAH(i, t4,  0);		/* 1: I3 + Q2*3 + Q1*3 + Q0 */
		int32_t sq0 = __SXTAH(q, t4, 16);		/* 1: Q3 + Q2*3 + Q1*3 + Q0 */
		i = __BFI(si0 / 8, sq0 / 8, 16, 16);	/* 1: D2_Q0:D2_I0 */
		*__SIMD32(d)++ = i;			/* D2_Q0:D2_I0 */

		i = __SXTH(t3, 0);			/* 1: I2 */
		q = __SXTH(t3, 16);			/* 1: Q2 */
		i = __SMLABB(t4, taps, i);	/* 1: I3*3 + I2 */
		q = __SMLATB(t4, taps, q);	/* 1: Q3*3 + Q2 */

		t1 = *__SIMD32(s)++;		/* 3: Q4:I4 */
		t2 = *__SIMD32(s)++;		/*    Q5:I5 */

		i = __SMLABB(t1, taps, i);	/* 1: I4*3 + I3*3 + I2 */
		q = __SMLATB(t1, taps, q);	/* 1: Q4*3 + Q3*3 + Q2 */
		int32_t si1 = __SXTAH(i, t2, 0) ;		/* 1: I5 + Q4*3 + Q3*3 + Q2 */
		int32_t sq1 = __SXTAH(q, t2, 16);		/* 1: Q5 + Q4*3 + Q3*3 + Q2 */
		i = __BFI(si1 / 8, sq1 / 8, 16, 16);	/* 1: D2_Q1:D2_I1 */
		*__SIMD32(d)++ = i;			/* D2_Q1:D2_I1 */
	}
	_iq0 = t1;
	_iq1 = t2;

	return { dst.p, src.count / 2, src.sampling_rate / 2 };
}

buffer_s16_t FIR64AndDecimateBy2Real::execute(
	buffer_s16_t src,
	buffer_s16_t dst
) {
	/* int16_t input (sample count "n" must be multiple of 4)
	 * -> int16_t output, decimated by 2.
	 * taps are normalized to 1 << 16 == 1.0.
	 */
	auto src_p = src.p;
	auto dst_p = dst.p;
	int32_t n = src.count;
	for(; n>0; n-=2) {
		z[taps_count-2] = *(src_p++);
		z[taps_count-1] = *(src_p++);

		int32_t t = 0;
		for(size_t j=0; j<taps_count; j+=4) {
			t += z[j+0] * taps[j+0];
			t += z[j+1] * taps[j+1];
			t += z[j+2] * taps[j+2];
			t += z[j+3] * taps[j+3];

			z[j+0] = z[j+0+2];
			z[j+1] = z[j+1+2];
			z[j+2] = z[j+2+2];
			z[j+3] = z[j+3+2];
		}
		*(dst_p++) = t / 65536;
	}

	return { dst.p, src.count / 2, src.sampling_rate / 2 };
}

buffer_c16_t FIRAndDecimateComplex::execute(
	buffer_c16_t src,
	buffer_c16_t dst
) {
	/* int16_t input (sample count "n" must be multiple of decimation_factor)
	 * -> int16_t output, decimated by decimation_factor.
	 * taps are normalized to 1 << 16 == 1.0.
	 */
	const auto output_sampling_rate = src.sampling_rate / decimation_factor_;
	const size_t output_samples = src.count / decimation_factor_;
	
	sample_t* dst_p = dst.p;
	const buffer_c16_t result { dst.p, output_samples, output_sampling_rate };

	const sample_t* src_p = src.p;
	size_t outer_count = output_samples;
	while(outer_count > 0) {
		/* Put new samples into delay buffer */
		auto z_new_p = &samples_[taps_count_ - decimation_factor_];
		for(size_t i=0; i<decimation_factor_; i++) {
			*__SIMD32(z_new_p)++ = *__SIMD32(src_p)++;
		}

		size_t loop_count = taps_count_ / 8;
		auto t_p = &taps_reversed_[0];
		auto z_p = &samples_[0];

		int64_t t_real = 0;
		int64_t t_imag = 0;

		while(loop_count > 0) {
			const auto tap0 = *__SIMD32(t_p)++;
			const auto sample0 = *__SIMD32(z_p)++;
			const auto tap1 = *__SIMD32(t_p)++;
			const auto sample1 = *__SIMD32(z_p)++;
			t_real = __SMLSLD(sample0, tap0, t_real);
			t_imag = __SMLALDX(sample0, tap0, t_imag);
			t_real = __SMLSLD(sample1, tap1, t_real);
			t_imag = __SMLALDX(sample1, tap1, t_imag);

			const auto tap2 = *__SIMD32(t_p)++;
			const auto sample2 = *__SIMD32(z_p)++;
			const auto tap3 = *__SIMD32(t_p)++;
			const auto sample3 = *__SIMD32(z_p)++;
			t_real = __SMLSLD(sample2, tap2, t_real);
			t_imag = __SMLALDX(sample2, tap2, t_imag);
			t_real = __SMLSLD(sample3, tap3, t_real);
			t_imag = __SMLALDX(sample3, tap3, t_imag);

			const auto tap4 = *__SIMD32(t_p)++;
			const auto sample4 = *__SIMD32(z_p)++;
			const auto tap5 = *__SIMD32(t_p)++;
			const auto sample5 = *__SIMD32(z_p)++;
			t_real = __SMLSLD(sample4, tap4, t_real);
			t_imag = __SMLALDX(sample4, tap4, t_imag);
			t_real = __SMLSLD(sample5, tap5, t_real);
			t_imag = __SMLALDX(sample5, tap5, t_imag);

			const auto tap6 = *__SIMD32(t_p)++;
			const auto sample6 = *__SIMD32(z_p)++;
			const auto tap7 = *__SIMD32(t_p)++;
			const auto sample7 = *__SIMD32(z_p)++;
			t_real = __SMLSLD(sample6, tap6, t_real);
			t_imag = __SMLALDX(sample6, tap6, t_imag);
			t_real = __SMLSLD(sample7, tap7, t_real);
			t_imag = __SMLALDX(sample7, tap7, t_imag);

			loop_count--;
		}

		/* TODO: Re-evaluate whether saturation is performed, normalization,
		 * all that jazz.
		 */
		const int32_t r = t_real >> 16;
		const int32_t i = t_imag >> 16;
		const int32_t r_sat = __SSAT(r, 16);
		const int32_t i_sat = __SSAT(i, 16);
		*__SIMD32(dst_p)++ = __PKHBT(
			r_sat,
			i_sat,
			16
		);

		/* Shift sample buffer left/down by decimation factor. */
		const size_t unroll_factor = 4;
		size_t shift_count = (taps_count_ - decimation_factor_) / unroll_factor;

		sample_t* t = &samples_[0];
		const sample_t* s = &samples_[decimation_factor_];
		
		while(shift_count > 0) {
			*__SIMD32(t)++ = *__SIMD32(s)++;
			*__SIMD32(t)++ = *__SIMD32(s)++;
			*__SIMD32(t)++ = *__SIMD32(s)++;
			*__SIMD32(t)++ = *__SIMD32(s)++;
			shift_count--;
		}

		shift_count = (taps_count_ - decimation_factor_) % unroll_factor;
		while(shift_count > 0) {
			*(t++) = *(s++);
			shift_count--;
		}

		outer_count--;
	}

	return result;
}

buffer_s16_t DecimateBy2CIC4Real::execute(
	buffer_s16_t src,
	buffer_s16_t dst
) {
	auto src_p = src.p;
	auto dst_p = dst.p;
	int32_t n = src.count;
	for(; n>0; n-=2) {
		/* TODO: Probably a lot of room to optimize... */
		z[0] = z[2];
		z[1] = z[3];
		z[2] = z[4];
		z[3] = *(src_p++);
		z[4] = *(src_p++);

		int32_t t = z[0] + z[1] * 4 + z[2] * 6 + z[3] * 4 + z[4];
		*(dst_p++) = t / 16;
	}

	return { dst.p, src.count / 2, src.sampling_rate / 2 };
}
#if 0
buffer_c16_t DecimateBy2HBF5Complex::execute(
	buffer_c16_t const src,
	buffer_c16_t const dst
) {
	auto src_p = src.p;
	auto dst_p = dst.p;
	int32_t n = src.count;
	for(; n>0; n-=2) {
		/* TODO: Probably a lot of room to optimize... */
		z[0] = z[2];
		//z[1] = z[3];
		z[2] = z[4];
		//z[3] = z[5];
		z[4] = z[6];
		z[5] = z[7];
		z[6] = z[8];
		z[7] = z[9];
		z[8] = z[10];
		z[9] = *(src_p++);
		z[10] = *(src_p++);

		int32_t t_real { z[5].real * 256 };
		int32_t t_imag { z[5].imag * 256 };
		t_real += (z[ 0].real + z[10].real) * 3;
		t_imag += (z[ 0].imag + z[10].imag) * 3;
		t_real -= (z[ 2].real + z[ 8].real) * 25;
		t_imag -= (z[ 2].imag + z[ 8].imag) * 25;
		t_real += (z[ 4].real + z[ 6].real) * 150;
		t_imag += (z[ 4].imag + z[ 6].imag) * 150;
		*(dst_p++) = { t_real / 256, t_imag / 256 };
	}

	return { dst.p, src.count / 2, src.sampling_rate / 2 };
}

buffer_c16_t DecimateBy2HBF7Complex::execute(
	buffer_c16_t const src,
	buffer_c16_t const dst
) {
	auto src_p = src.p;
	auto dst_p = dst.p;
	int32_t n = src.count;
	for(; n>0; n-=2) {
		/* TODO: Probably a lot of room to optimize... */
		z[0] = z[2];
		//z[1] = z[3];
		z[2] = z[4];
		//z[3] = z[5];
		z[4] = z[6];
		z[5] = z[7];
		z[6] = z[8];
		z[7] = z[9];
		z[8] = z[10];
		z[9] = *(src_p++);
		z[10] = *(src_p++);

		int32_t t_real { z[5].real * 512 };
		int32_t t_imag { z[5].imag * 512 };
		t_real += (z[ 0].real + z[10].real) * 7;
		t_imag += (z[ 0].imag + z[10].imag) * 7;
		t_real -= (z[ 2].real + z[ 8].real) * 53;
		t_imag -= (z[ 2].imag + z[ 8].imag) * 53;
		t_real += (z[ 4].real + z[ 6].real) * 302;
		t_imag += (z[ 4].imag + z[ 6].imag) * 302;
		*(dst_p++) = { t_real / 512, t_imag / 512 };
	}

	return { dst.p, src.count / 2, src.sampling_rate / 2 };
}
#endif
} /* namespace decimate */
} /* namespace dsp */