Adding documentation

Copied from VOLK, with some minor changes

src/algorithms/libs/volk_gnsssdr_module/volk_gnsssdr/docs/extending_volk.dox

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+/*! \page extending_volk Extending VOLK
+
+There are two primary routes for extending VOLK for your own use. The
+preferred route is by writing kernels and proto-kernels as part of this
+repository and sending patches upstream. The alternative is creating your
+own VOLK module, as it is the case of VOLK_GNSSSDR ;-). There is a good reason
+for that: to provide GNSS-SDR users with adequate protokernels as soon as possible, 
+without needing to upgrade to the latest VOLK version to enjoy the benefits. 
+Notwithstanding, some of VOLK_GNSSSDR can be integrated into VOLK in the future,
+if other users find them useful.
+
+## Modifying this repository
+
+### Adding kernels
+
+Adding kernels refers to introducing a new function to the VOLK API that is
+presumably a useful math function/operation. The first step is to create
+the file in volk/kernels/volk. Follow the naming scheme provided in the
+VOLK terms and techniques page. First create the generic protokernel.
+
+The generic protokernel should be written in plain C using explicitly sized
+types from stdint.h or volk_complex.h when appropriate. volk_complex.h
+includes explicitly sized complex types for floats and ints. The name of
+the generic kernel should be volk_signature_from_file_generic. If multiple
+versions of the generic kernel exist then a description can be appended to
+generic_, but it is not required to use alignment flags in the generic
+protokernel name. It is required to surround the entire generic function
+with preprocessor ifdef fences on the symbol LV_HAVE_GENERIC.
+
+Finally, add the kernel to the list of test cases in volk/lib/kernel_tests.h.
+Many kernels should be able to use the default test parameters, but if yours
+requires a lower tolerance, specific vector length, or other test parameters
+just create a new instance of volk_test_params_t for your kernel.
+
+### Adding protokernels
+
+The primary purpose of VOLK is to have multiple implementations of an operation
+tuned for a specific CPU architecture. Ideally there is at least one
+protokernel of each kernel for every architecture that VOLK supports.
+The pattern for protokernel naming is volk_kernel_signature_architecture_nick.
+The architecture should be one of the supported VOLK architectures. The nick is
+an optional name to distinguish between multiple implementations for a
+particular architecture.
+
+Architecture specific protokernels can be written in one of three ways.
+The first approach should always be to use compiler intrinsic functions.
+The second and third approaches are using either in-line assembly or
+assembly with .S files. Both methods of writing assembly exist in VOLK and
+should yield equivalent performance; which method you might choose is a
+matter of opinion. Regardless of the actual method the public function should
+be declared in the kernel header surrounded by ifdef fences on the symbol that
+fits the architecture implementation.
+
+#### Compiler Intrinsics
+
+Compiler intrinsics should be treated as functions that map to a specific
+assembly instruction. Most VOLK kernels take the form of a loop that iterates
+through a vector. Form a loop that iterates on a number of items that is natural
+for the architecture and then use compiler intrinsics to do the math for your
+operation or algorithm. Include the appropriate header inside the ifdef fences,
+but before your protokernel declaration.
+
+
+#### In-line Assembly
+
+In-line assembly uses a compiler macro to include verbatim assembly with C code.
+The process of in-line assembly protokernels is very similar to protokernels
+based on intrinsics.
+
+#### Assembly with .S files
+
+To write pure assembly protokernels, first declare the function name in the
+kernel header file the same way as any other protokernel, but include the extern
+keyword. Second, create a file (one for each protokernel) in
+volk/kernels/volk/asm/$arch. Disassemble another protokernel and copy the
+disassembled code in to this file to bootstrap a working implementation. Often
+the disassembled code can be hand-tuned to improve performance.
+
+## VOLK Modules
+
+VOLK has a concept of modules. Each module is an independent VOLK tree. Modules
+can be managed with the volk_modtool application. At a high level the module is
+a clone of all of the VOLK machinery without kernels. volk_modtool also makes it
+easy to copy kernels to a module.
+
+Kernels and protokernels are added to your own VOLK module the same way they are
+added to this repository, which was described in the previous section.
+
+VOLK_GNSSSDR is a VOLK Module.
+
+*/
+

src/algorithms/libs/volk_gnsssdr_module/volk_gnsssdr/docs/kernels.dox

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+/*! \page kernels Kernels
+
+\li \subpage volk_gnsssdr_32fc_convert_16ic
+\li \subpage volk_gnsssdr_32fc_convert_8ic
+\li \subpage volk_gnsssdr_16ic_convert_32fc
+\li \subpage volk_gnsssdr_16ic_resampler_16ic
+\li \subpage volk_gnsssdr_16ic_xn_resampler_16ic_xn
+\li \subpage volk_gnsssdr_16ic_s32fc_x2_rotator_16ic
+\li \subpage volk_gnsssdr_16ic_x2_multiply_16ic
+\li \subpage volk_gnsssdr_16ic_x2_dot_prod_16ic
+\li \subpage volk_gnsssdr_16ic_x2_dot_prod_16ic_xn
+\li \subpage volk_gnsssdr_16ic_x2_rotator_dot_prod_16ic_xn
+\li \subpage volk_gnsssdr_8i_accumulator_s8i
+\li \subpage volk_gnsssdr_8i_index_max_16u
+\li \subpage volk_gnsssdr_8i_max_s8i
+\li \subpage volk_gnsssdr_8i_x2_add_8i
+\li \subpage volk_gnsssdr_8ic_conjugate_8ic
+\li \subpage volk_gnsssdr_8ic_magnitude_squared_8i
+\li \subpage volk_gnsssdr_8ic_x2_dot_prod_8ic
+\li \subpage volk_gnsssdr_8ic_x2_multiply_8ic
+\li \subpage volk_gnsssdr_8ic_s8ic_multiply_8ic
+\li \subpage volk_gnsssdr_64f_accumulator_64f
+
+*/

src/algorithms/libs/volk_gnsssdr_module/volk_gnsssdr/docs/main_page.dox

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+/*! \mainpage VOLK_GNSSSDR
+
+Welcome to VOLK_GNSSSDR!
+
+VOLK_GNSSSDR is the Vector-Optimized Library of Kernels for GNSS-SDR. 
+It is a library that contains kernels of hand-written SIMD code for different 
+mathematical operations. Since each SIMD architecture can be very different 
+and no compiler has yet come along to handle vectorization properly or highly 
+efficiently, VOLK_GNSSSDR approaches the problem differently.
+
+For each architecture or platform that a developer wishes to vectorize for, a
+new proto-kernel is added to VOLK_GNSSSDR. At runtime, VOLK_GNSSSDR will select the correct
+proto-kernel. In this way, the users of VOLK_GNSSSDR call a kernel for performing the
+operation that is platform/architecture agnostic. This allows us to write
+portable SIMD code.
+
+VOLK_GNSSSDR is a module generated from the original VOLK library http://libvolk.org
+
+*/

src/algorithms/libs/volk_gnsssdr_module/volk_gnsssdr/docs/terms_and_techniques.dox

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+/*! \page concepts_terms_and_techniques Concepts, Terms, and Techniques
+
+This page is primarily a list of definitions and brief overview of successful
+techniques previously used to develop VOLK_GNSSSDR protokernels.
+
+## Definitions and Concepts
+
+### SIMD
+
+SIMD stands for Single Instruction Multiple Data. Leveraging SIMD instructions
+is the primary optimization in VOLK_GNSSSDR.
+
+### Architecture
+
+A VOLK_GNSSSDR architecture is normally called an Instruction Set Architecture (ISA).
+The architectures we target in VOLK_GNSSSDR usually have SIMD instructions.
+
+### Vector
+
+A vector in VOLK_GNSSSDR is the same as a C array. It sometimes, but not always
+coincides with the mathematical definition of a vector.
+
+### Kernel
+
+The 'kernel' part of the VOLK_GNSSSDR name comes from the high performance computing
+use of the word. In this context it is the inner loop of a vector operation.
+Since we don't use the word vector in the math sense a vector operation is an
+operation that is performed on a C array.
+
+### Protokernel
+
+A protokernel is an implementation of a kernel. Every kernel has a 'generic'
+protokernel that is implemented in C. Other protokernels are optimized for a
+particular architecture.
+
+
+## Techniques
+
+### New Kernels
+
+Add new kernels to the list in lib/kernel_tests.h. This adds the kernel to
+VOLK_GNSSSDR's QA tool as well as the volk profiler. Many kernels are able to
+share test parameters, but new kernels might need new ones.
+
+If the VOLK_GNSSSDR kernel does not 'fit' the the standard set of function parameters
+expected by the volk_profile structure, you need to create a VOLK_GNSSSDR puppet
+function to help the profiler call the kernel. This is essentially due to the
+function run_volk_gnsssdr_tests which has a limited number of function prototypes that
+it can test.
+
+### Protokernels
+
+Adding new proto-kernels (implementations of VOLK_GNSSSDR kernels for specific
+architectures) is relatively easy. In the relevant <kernel>.h file in
+the volk_gnsssdr/include/volk_gnsssdr/volk_gnsssdr<input-fingerprint_function-name_output-fingerprint>.h
+file, add a new #ifdef/#endif block for the LV_HAVE_<arch> corresponding
+to the <arch> you a working on (e.g. SSE, AVX, NEON, etc.).
+
+For example, for volk_gnsssdr_16ic_x2_multiply_16ic_neon:
+
+\code
+#ifdef LV_HAVE_NEON
+#include <arm_neon.h>
+
+static inline void volk_gnsssdr_16ic_x2_multiply_16ic_neon(lv_16sc_t* out, const lv_16sc_t* in_a, const lv_16sc_t* in_b, unsigned int num_points)
+{
+    lv_16sc_t *a_ptr = (lv_16sc_t*) in_a;
+    lv_16sc_t *b_ptr = (lv_16sc_t*) in_b;
+    unsigned int quarter_points = num_points / 4;
+    int16x4x2_t a_val, b_val, c_val;
+    int16x4x2_t tmp_real, tmp_imag;
+    unsigned int number = 0;
+
+    for(; number < quarter_points; ++number)
+        {
+            a_val = vld2_s16((int16_t*)a_ptr);
+            b_val = vld2_s16((int16_t*)b_ptr);
+
+            tmp_real.val[0] = vmul_s16(a_val.val[0], b_val.val[0]);
+            tmp_real.val[1] = vmul_s16(a_val.val[1], b_val.val[1]);
+
+            tmp_imag.val[0] = vmul_s16(a_val.val[0], b_val.val[1]);
+            tmp_imag.val[1] = vmul_s16(a_val.val[1], b_val.val[0]);
+
+            c_val.val[0] = vsub_s16(tmp_real.val[0], tmp_real.val[1]);
+            c_val.val[1] = vadd_s16(tmp_imag.val[0], tmp_imag.val[1]);
+            vst2_s16((int16_t*)out, c_val);
+
+            a_ptr += 4;
+            b_ptr += 4;
+            out += 4;
+        }
+
+    for(number = quarter_points * 4; number < num_points; number++)
+        {
+            *out++ = (*a_ptr++) * (*b_ptr++);
+        }
+}
+#endif /* LV_HAVE_NEON */
+\endcode
+
+### Allocating Memory
+
+SIMD code can be very sensitive to the alignment of the vectors, which is
+generally something like a 16-byte or 32-byte alignment requirement. The
+VOLK_GNSSSDR dispatcher functions, which is what we will normally call as users of
+VOLK_GNSSSDR, makes sure that the correct aligned or unaligned version is called
+depending on the state of the vectors passed to it. However, things typically
+work faster and more efficiently when the vectors are aligned. As such, VOLK_GNSSSDR
+has memory allocate and free methods to provide us with properly aligned
+vectors. We can also ask VOLK_GNSSSDR to give us the current machine's alignment
+requirement, which makes our job even easier when porting code.
+
+To get the machine's alignment, simply call the size_t volk_gnsssdr_get_alignment().
+
+Allocate memory using void* volk_gnsssdr_malloc(size_t size, size_t alignment).
+
+Make sure that any memory allocated by VOLK_GNSSSDR is also freed by VOLK_GNSSSDR with volk_gnsssdr_free(void *p).
+
+
+*/

src/algorithms/libs/volk_gnsssdr_module/volk_gnsssdr/docs/using_volk_gnsssdr.dox

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+/*! \page using_volk_gnsssdr Using VOLK_GNSSSDR
+
+Using VOLK_GNSSSDR in your code requires proper linking and including the correct headers. 
+VOLK_GNSSSDR currently supports both C and C++ bindings.
+
+VOLK_GNSSSDR provides both a pkgconfig and CMake module to help configuration and
+linking. The pkfconfig file is installed to
+$install_prefix/lib/pkgconfig/volk_gnsssdr.pc. The CMake configuration module is in
+$install_prefix/lib/cmake/volk_gnsssdr/VolkConfig.cmake.
+
+The header in the VOLK_GNSSSDR include directory (includedir in pkgconfig,
+VOLK_GNSSSDR_INCLUDE_DIRS in cmake module) contains the header volk_gnsssdr/volk_gnsssdr.h defines all
+of the symbols exposed by VOLK_GNSSSDR. Alternatively individual kernel headers are in
+the same location.
+
+In most cases it is sufficient to call the dispatcher for the kernel you are using.
+
+*/
+

src/algorithms/libs/volk_gnsssdr_module/volk_gnsssdr/kernels/volk_gnsssdr/volk_gnsssdr_16ic_convert_32fc.h

@@ -1,6 +1,6 @@
 /*!
- * \file volk_gnsssdr_32fc_convert_16ic.h
- * \brief Volk protokernel: converts 16 bit integer complex complex values to  32 bits float complex values
+ * \file volk_gnsssdr_16ic_convert_32fc.h
+ * \brief Volk protokernel: converts 16 bit integer complex complex values to 32 bits float complex values
  * \authors <ul>
  *          <li> Javier Arribas, 2015. jarribas(at)cttc.es
  *          </ul>