### rs_sig_begin()

Source: https://librsync.github.io/mksum_8c.html

Starts generating a signature. It is recommended to use rs_sig_args() to get the recommended arguments based on the original file size. Returns a new rs_job_t into which the old file data can be passed.

```APIDOC
## rs_sig_begin()

### Description
Starts generating a signature. It is recommended to use rs_sig_args() to get the recommended arguments based on the original file size.

### Function Signature
rs_job_t * rs_sig_begin(size_t block_len, size_t strong_len, rs_magic_number sig_magic)

### Parameters
- **sig_magic** (rs_magic_number) - Required - Signature file format to generate (0 for "recommended"). See rs_magic_number.
- **block_len** (size_t) - Required - Checksum block size to use (0 for "recommended"). Larger values make the signature shorter, and the delta longer.
- **strong_len** (size_t) - Required - Strongsum length in bytes to use (0 for "maximum", -1 for "minimum"). Smaller values make the signature shorter but increase the risk of corruption from hash collisions.

### Returns
A new rs_job_t into which the old file data can be passed.

### See Also
rs_sig_file()
```

--------------------------------

### Install librsync with sudo make install

Source: https://librsync.github.io/page_install.html

Install librsync and rdiff system-wide using sudo make install.

```bash
$ sudo make install

```

--------------------------------

### Install libpopt on Windows via vcpkg

Source: https://librsync.github.io/md_CONTRIBUTING.html

Commands to update vcpkg and install the libpopt library for native Windows development.

```bash
$ vcpkg update
$ vcpkg --triplet x64-windows install libpopt
```

--------------------------------

### rs_sig_begin

Source: https://librsync.github.io/mksum_8c_source.html

Starts generating a signature for a file.

```APIDOC
## rs_sig_begin

### Description
Start generating a signature. This function initializes a new signature job.

### Function Signature
`rs_job_t * rs_sig_begin(size_t block_len, size_t strong_len, rs_magic_number sig_magic)`

### Parameters
- **block_len** (size_t) - Required - The block length for the signature.
- **strong_len** (size_t) - Required - The strong sum length.
- **sig_magic** (rs_magic_number) - Required - The magic number for the signature.

### Returns
- **rs_job_t \*** - A new signature job.

### Definition
mksum.c:110
```

--------------------------------

### Install libpopt on MacOS via Homebrew

Source: https://librsync.github.io/md_CONTRIBUTING.html

Commands to update Homebrew and install the popt library.

```bash
$ brew update
$ brew install popt
```

--------------------------------

### Install development dependencies on Debian/Ubuntu

Source: https://librsync.github.io/md_CONTRIBUTING.html

Commands to update package lists, install required development libraries and tools, and set up the tidyc utility.

```bash
$ apt-get update
$ apt-get install libpopt-dev libb2-dev doxygen graphviz indent clang-tidy iwyu
$ git clone https://github.com/dbaarda/tidyc.git
$ cp tidyc/tidyc ~/bin
```

--------------------------------

### Basic hashtable usage with ENTRY and KEY macros

Source: https://librsync.github.io/hashtable_8h.html

Shows how to define a custom entry type and configure the hashtable using the ENTRY and KEY macros. The example creates a hashtable, adds an entry, finds it, iterates, and frees it.

```c
typedef ... mykey_t;
int mykey_hash(mykey_t const *e);
int mykey_cmp(mykey_t *e, mykey_t const *o);
typedef struct myentry {
mykey_t key; // Inherit from mykey_t.
...extra entry value data...
} myentry_t;
void myentry_init(myentry_t *e, ...);
#define ENTRY myentry
#define KEY mykey
#include "hashtable.h"
hashtable_t *t;
myentry_t entries[300];
mykey_t k;
myentry_t *e;
t = myentry_hashtable_new(300);
myentry_init(&entries[5], ...);
myentry_hashtable_add(t, &entries[5]);
k = ...;
e = myentry_hashtable_find(t, &k);
int i;
for (e = myentry_hashtable_iter(t, &i); e != NULL;
e = myentry_hashtable_next(t, &i))
...
myentry_hashtable_free(t);
```

--------------------------------

### rdiff_show_version function start

Source: https://librsync.github.io/rdiff_8c_source.html

Function rdiff_show_version begins by declaring empty strings for bzlib, zlib, and trace, then enters a preprocessor block that is disabled with #if 0. The function is incomplete in the source.

```c
static void rdiff_show_version(void)
{
 char const *bzlib = "", *zlib = "", *trace = "";

#if 0
```

--------------------------------

### rs_sig_args function (partial)

Source: https://librsync.github.io/sumset_8c_source.html

Starts the rs_sig_args function, which calculates recommended block and strong lengths based on the old file size. The snippet is incomplete as shown in the source.

```c
rs_result rs_sig_args(rs_long_t old_fsize, rs_magic_number * magic,
 size_t *block_len, size_t *strong_len)
{
 size_t rec_block_len; /* the recomended block_len for the given
 old_fsize. */
 size_t min_strong_len; /* the minimum strong_len for the given
```

--------------------------------

### Begin loading signature

Source: https://librsync.github.io/readsums_8c_source.html

Initializes the job for loading a signature.

```c
rs_job_t *rs_loadsig_begin(rs_signature_t **signature)
{
 rs_job_t *job;

```

--------------------------------

### Build documentation with make doc

Source: https://librsync.github.io/page_install.html

Run make doc to build the documentation (requires Doxygen).

```bash
$ make doc

```

--------------------------------

### rs_scoop_nextbuf

Source: https://librsync.github.io/scoop_8h_source.html

Get the next iteration of contiguous data buffers from the scoop. Advances the scoop for the previous iteration and gets the next iteration.

```APIDOC
## rs_scoop_nextbuf

### Description
Get the next iteration of contiguous data buffers from the scoop. Advances the scoop for the previous iteration and gets the next iteration.

### Function Signature
static void *rs_scoop_nextbuf(rs_job_t *job, size_t *len, size_t *ilen)

### Parameters
- **job** (rs_job_t *) - Required - The job instance to use.
- **len** (size_t *) - Required - The size_t amount of data to iterate over.
- **ilen** (size_t *) - Required - The size_t amount of data in the current iteration.

### Return Value
void * - A pointer to data in the current iteration.

### Definition
scoop.h:175
```

--------------------------------

### Enable compression with ENABLE_COMPRESSION=ON

Source: https://librsync.github.io/page_install.html

Compression support is disabled by default; set ENABLE_COMPRESSION to ON to enable it.

```bash
$ cmake -D ENABLE_COMPRESSION=ON .

```

--------------------------------

### rs_signature_strongsum_kind

Source: https://librsync.github.io/sumset_8h.html

Gets the strongsum kind for a signature.

```APIDOC
## rs_signature_strongsum_kind

### Description
Gets the strongsum kind for a signature.

### Function Signature
static strongsum_kind_t rs_signature_strongsum_kind(rs_signature_t const *sig)

### Parameters
- **sig** (rs_signature_t const *) - Required - Pointer to the signature instance.

### Return Value
- **strongsum_kind_t** - The strongsum kind.
```

--------------------------------

### Build and run tests with make check

Source: https://librsync.github.io/page_install.html

Run make check to build and run the test suite.

```bash
$ make check

```

--------------------------------

### rs_signature_weaksum_kind

Source: https://librsync.github.io/sumset_8h.html

Gets the weaksum kind for a signature.

```APIDOC
## rs_signature_weaksum_kind

### Description
Gets the weaksum kind for a signature.

### Function Signature
static weaksum_kind_t rs_signature_weaksum_kind(rs_signature_t const *sig)

### Parameters
- **sig** (rs_signature_t const *) - Required - Pointer to the signature instance.

### Return Value
- **weaksum_kind_t** - The weaksum kind.
```

--------------------------------

### Use Ninja as the build tool

Source: https://librsync.github.io/page_install.html

Generate Ninja build files and run the check target with ninja.

```bash
$ cmake -G Ninja .
$ ninja check

```

--------------------------------

### rs_emit_delta_header

Source: https://librsync.github.io/emit_8h.html

Writes the magic for the start of a delta.

```APIDOC
## rs_emit_delta_header

### Description
Writes the magic for the start of a delta.

### Function Signature
void rs_emit_delta_header(rs_job_t *job)

### Parameters
- **job** (rs_job_t *) - Required - Pointer to the job context.

### Returns
void
```

--------------------------------

### rs_delta_begin function

Source: https://librsync.github.io/delta_8c_source.html

Initializes a new delta encoding job, optionally setting up a signature for matching.

```c
rs_job_t *rs_delta_begin(rs_signature_t *sig)
{
 rs_job_t *job;

 job = rs_job_new("delta", rs_delta_s_header);
 /* Caller can pass NULL sig or empty sig for "slack deltas". */
 if (sig && sig->count > 0) {
 rs_signature_check(sig);
 /* Caller must have called rs_build_hash_table() by now. */
 assert(sig->hashtable);
 job->signature = sig;
 weaksum_init(&job->weak_sum, rs_signature_weaksum_kind(sig));
 }
 return job;
}
```

--------------------------------

### rs_scoop_buf

Source: https://librsync.github.io/scoop_8h_source.html

Get a pointer to the next input in the scoop.

```APIDOC
## rs_scoop_buf

### Description
Get a pointer to the next input in the scoop.

### Function Signature
static inline void *rs_scoop_buf(rs_job_t *job)

### Parameters
- **job** (rs_job_t *) - Required - The job instance to use.

### Return Value
void * - Pointer to the next input data.

### Definition
scoop.h:106
```

--------------------------------

### rs_scoop_avail

Source: https://librsync.github.io/scoop_8h_source.html

Get the amount of data available in the scoop.

```APIDOC
## rs_scoop_avail

### Description
Get the amount of data available in the scoop.

### Function Signature
static inline size_t rs_scoop_avail(rs_job_t *job)

### Parameters
- **job** (rs_job_t *) - Required - The job instance to use.

### Return Value
size_t - The number of bytes available.

### Definition
scoop.h:94
```

--------------------------------

### main function for rdiff

Source: https://librsync.github.io/rdiff_8c_source.html

Initializes the popt context, parses command-line options, and executes the requested rdiff action.

```c
int main(const int argc, const char *argv[])
{
 /* Initialize opts at runtime to avoid unknown address values. */
 const struct poptOption opts[] = {
 {"verbose", 'v', POPT_ARG_NONE, 0, 'v'},
 {"version", 'V', POPT_ARG_NONE, 0, 'V'},
 {"input-size", 'I', POPT_ARG_INT, &rs_inbuflen},
 {"output-size", 'O', POPT_ARG_INT, &rs_outbuflen},
 {"hash", 'H', POPT_ARG_STRING, &rs_hash_name},
 {"rollsum", 'R', POPT_ARG_STRING, &rs_rollsum_name},
 {"help", '?', POPT_ARG_NONE, 0, 'h'},
 {0, 'h', POPT_ARG_NONE, 0, 'h'},
 {"block-size", 'b', POPT_ARG_INT, &block_len},
 {"sum-size", 'S', POPT_ARG_INT, &strong_len},
 {"statistics", 's', POPT_ARG_NONE, &show_stats},
 {"stats", 0, POPT_ARG_NONE, &show_stats},
 {"gzip", 'z', POPT_ARG_NONE, 0, OPT_GZIP},
 {"bzip2", 'i', POPT_ARG_NONE, 0, OPT_BZIP2},
 {"force", 'f', POPT_ARG_NONE, &file_force},
 {0}
 };

 poptContext opcon;
 rs_result result;

 opcon = poptGetContext("rdiff", argc, argv, opts, 0);
 rdiff_options(opcon);
 result = rdiff_action(opcon);

 if (result != RS_DONE)
 fprintf(stderr, "rdiff: Failed, %s.\n", rs_strerror(result));

 poptFreeContext(opcon);
 return result;
}
```

--------------------------------

### rs_scoop_len

Source: https://librsync.github.io/scoop_8h_source.html

Get the contiguous length of the next input in the scoop.

```APIDOC
## rs_scoop_len

### Description
Get the contiguous length of the next input in the scoop.

### Function Signature
static inline size_t rs_scoop_len(rs_job_t *job)

### Parameters
- **job** (rs_job_t *) - Required - The job instance to use.

### Return Value
size_t - The contiguous length of the next input.

### Definition
scoop.h:113
```

--------------------------------

### rs_file_size

Source: https://librsync.github.io/fileutil_8c_source.html

Gets the size of a file. Returns the size as a rs_long_t.

```APIDOC
## rs_file_size

### Description
Gets the size of a file.

### Signature
`LIBRSYNC_EXPORT rs_long_t rs_file_size(FILE *file)`

### Parameters
- **file** (FILE*) - Required - The file stream to query.

### Returns
- **rs_long_t** - The size of the file.

### Definition
fileutil.c:127
```

--------------------------------

### Perform a custom Release build with Ninja

Source: https://librsync.github.io/md_CONTRIBUTING.html

Configure a build in a separate directory using specific compiler, build type, and library settings, followed by the build and test command.

```bash
$ cmake -B build -G Ninja
-D CMAKE_C_COMPILER=clang \
-D CMAKE_BUILD_TYPE=Release \
-D BUILD_SHARED_LIBS=OFF \
-D USE_LIBB2=ON \
-D ENABLE_TRACE=ON
$ cmake --build build --config Release --target check
```

--------------------------------

### C++ example for Doxygen graph legend

Source: https://librsync.github.io/graph_legend.html

C++ class definitions used to illustrate Doxygen graph conventions. The example includes documented, undocumented, and truncated classes, plus public, protected, and private inheritance, a template class, and a usage relation. The resulting graph is shown below the code.

```cpp
/*! Invisible class because of truncation */
class Invisible { };
/*! Truncated class, inheritance relation is hidden */
class Truncated : public Invisible { };
/* Class not documented with doxygen comments */
class Undocumented { };
/*! Class that is inherited using public inheritance */
class PublicBase : public Truncated { };
/*! A template class */
template<class T> class Templ { };
/*! Class that is inherited using protected inheritance */
class ProtectedBase { };
/*! Class that is inherited using private inheritance */
class PrivateBase { };
/*! Class that is used by the Inherited class */
class Used { };
/*! Super class that inherits a number of other classes */
class Inherited : public PublicBase,
protected ProtectedBase,
private PrivateBase,
public Undocumented,
public Templ<int>
{
private:
Used *m_usedClass;
};
```

--------------------------------

### Build librsync with make

Source: https://librsync.github.io/page_install.html

After generating the Makefile, run make to build librsync and rdiff.

```bash
$ make

```

--------------------------------

### rs_magic_number

Source: https://librsync.github.io/librsync_8h_source.html

A uint32 magic number, emitted in bigendian/network order at the start of librsync files.

```APIDOC
## rs_magic_number

### Description
A uint32 magic number, emitted in bigendian/network order at the start of librsync files.

### Values
- **RS_DELTA_MAGIC** - A delta file.
- **RS_MD4_SIG_MAGIC** - A signature file with MD4 signatures.
- **RS_BLAKE2_SIG_MAGIC** - A signature file using the BLAKE2 hash.
- **RS_RK_MD4_SIG_MAGIC** - A signature file with RabinKarp rollsum and MD4 hash.
- **RS_RK_BLAKE2_SIG_MAGIC** - A signature file with RabinKarp rollsum and BLAKE2 hash.
```

--------------------------------

### rs_file_size

Source: https://librsync.github.io/librsync_8h_source.html

Gets the size of a file in a platform-independent way. Returns -1 if the size cannot be determined because it is not a regular file.

```APIDOC
## rs_file_size

### Description
Gets the size of a file in a platform-independent way. Returns -1 if the size cannot be determined because it is not a regular file.

### Function Signature
rs_long_t rs_file_size(FILE *file)

### Parameters
- **file** (FILE *) - Required - The stdio file to get the size of.

### Returns
rs_long_t - The file size, or -1 if not a regular file.
```

--------------------------------

### NAME_new

Source: https://librsync.github.io/hashtable_8h_source.html

Initializes a new hashtable instance with a specified minimum size.

```c
static inline hashtable_t *NAME_new(int size)
{
 return _hashtable_new(size);
}
```

--------------------------------

### Non-docbook comment styles

Source: https://librsync.github.io/md_CONTRIBUTING.html

Examples of preferred formatting for non-docbook comments, including block and inline styles.

```c
/*=
| A short poem that
| shall never ever be
| reformated or reindented
*/
/* Single line comment indented to match code indenting. */
/* Blank line delimited paragraph multi-line comments.
Without leading stars, or blank line comment delimiters. */
int a; /* code line comments */
```

--------------------------------

### NAME_next()

Source: https://librsync.github.io/hashtable_8h.html

Gets the next entry from a hashtable iterator or NULL when finished. Works together with NAME_iter() for iterating through all entries.

```APIDOC
## NAME_next()

### Description
Gets the next entry from a hashtable iterator or NULL when finished. Works together with NAME_iter() for iterating through all entries.

### Function Signature
static ENTRY_t * NAME_next(hashtable_t *t, int *i)

### Parameters
- **t** (hashtable_t *) - Required - The hashtable to iterate over.
- **i** (int *) - Required - The int iterator index to use.

### Returns
The next entry or NULL if the iterator is finished.
```

--------------------------------

### rs_loadsig_begin()

Source: https://librsync.github.io/api_streaming.html

Loads a signature into memory. This function initiates a load signature job.

```APIDOC
## rs_loadsig_begin()

### Description
Loads a signature into memory. This function initiates a load signature job.

### Method
Function

### Endpoint
rs_loadsig_begin()

### Parameters
None explicitly documented.

### Request Example
No request body.

### Response
#### Success Response
Returns a rs_job_t object.

#### Response Example
No response body example provided.
```

--------------------------------

### rs_sig_begin()

Source: https://librsync.github.io/api_streaming.html

Calculates the signature of a file. This function initiates a signature job.

```APIDOC
## rs_sig_begin()

### Description
Calculates the signature of a file. This function initiates a signature job.

### Method
Function

### Endpoint
rs_sig_begin()

### Parameters
None explicitly documented.

### Request Example
No request body.

### Response
#### Success Response
Returns a rs_job_t object.

#### Response Example
No response body example provided.
```

--------------------------------

### Copy command format

Source: https://librsync.github.io/page_formats.html

Encoding of a copy command in a delta file: a command byte (0x45-0x54), a start offset, and a length, all big-endian.

```c
u8 command; // in the range 0x45 through 0x54 inclusive
u8[arg1_len] start; // offset in the basis to begin copying data
u8[arg2_len] length; // number of bytes to copy from the basis
```

--------------------------------

### Configure build interactively

Source: https://librsync.github.io/md_CONTRIBUTING.html

Use the ccmake tool to interactively configure the project in a separate build directory.

```bash
$ ccmake -B build
```

--------------------------------

### rs_sig_args()

Source: https://librsync.github.io/api_streaming.html

Gets the recommended signature arguments from the input file's size. This helper function can be used to obtain recommended signature arguments.

```APIDOC
## rs_sig_args()

### Description
Gets the recommended signature arguments from the input file's size. This helper function can be used to obtain recommended signature arguments.

### Method
Function

### Endpoint
rs_sig_args()

### Parameters
None explicitly documented.

### Request Example
No request body.

### Response
#### Success Response
Returns the recommended signature arguments.

#### Response Example
No response body example provided.
```

--------------------------------

### Configure CMake for vcpkg on Windows

Source: https://librsync.github.io/md_CONTRIBUTING.html

Required flag to add to the cmake command line to ensure CMake locates libraries installed via vcpkg.

```bash
-D CMAKE_TOOLCHAIN_FILE=C:/vcpkg/scripts/buildsystems/vcpkg.cmake
```

--------------------------------

### Perform a default Debug build

Source: https://librsync.github.io/md_CONTRIBUTING.html

The minimal sequence of commands to clone, configure, and test the project using default settings.

```bash
$ git clone https://github.com/librsync/librsync.git
$ cd librsync
$ cmake .
$ make check
```

--------------------------------

### rs_scoop_getbuf

Source: https://librsync.github.io/scoop_8h_source.html

Get the next contiguous buffer of data available in the scoop. Returns a pointer to the data and reduces len to the amount of contiguous data available.

```APIDOC
## rs_scoop_getbuf

### Description
Get the next contiguous buffer of data available in the scoop. Returns a pointer to the data and reduces len to the amount of contiguous data available.

### Function Signature
static void *rs_scoop_getbuf(rs_job_t *job, size_t *len)

### Parameters
- **job** (rs_job_t *) - Required - The job instance to use.
- **len** (size_t *) - Required - The amount of data desired, updated to the amount available.

### Return Value
void * - A pointer to the data.

### Definition
scoop.h:128
```

--------------------------------

### rs_delta_begin

Source: https://librsync.github.io/librsync_8h_source.html

Prepares to compute a streaming delta.

```APIDOC
## rs_delta_begin

### Description
Prepares to compute a streaming delta.

### Function Signature
rs_job_t *rs_delta_begin(rs_signature_t *)

### Parameters
- **signature** (rs_signature_t*) - Required - The signature to use for delta computation.

### Return Value
- **rs_job_t*** - A new job for delta computation.

### Notes
- Todo: Add a version of this that takes a ::rs_magic_number controlling the delta format.
```

--------------------------------

### trace.c: librsync trace module implementation

Source: https://librsync.github.io/trace_8c_source.html

Complete source of trace.c, implementing the trace callback system, severity levels, and message formatting. Includes the default stderr callback and a compile-time check for trace support.

```c
/*= -*- c-basic-offset: 4; indent-tabs-mode: nil; -*-
 *
 * librsync -- library for network deltas
 *
 * Copyright (C) 2000, 2001 by Martin Pool <mbp@sourcefrog.net>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

 /*=
 | Finality is death.
 | Perfection is finality.
 | Nothing is perfect.
 | There are lumps in it.
 */

#include "config.h" /* IWYU pragma: keep */
#include <stdio.h>
#include <stdarg.h>
#include "librsync.h"
#include "trace.h"
#include "util.h"

rs_trace_fn_t *rs_trace_impl = rs_trace_stderr;

int rs_trace_level = RS_LOG_INFO;

#define MY_NAME "librsync"

static void rs_log_va(int level, char const *fn, char const *fmt, va_list va);

/** Log severity strings, if any. Must match ordering in ::rs_loglevel. */
static const char *rs_severities[] = {
 "EMERGENCY! ", "ALERT! ", "CRITICAL! ", "ERROR: ", "Warning: ",
 "", "", ""
};

/** Set the destination of trace information.
 *
 * The callback scheme allows for use within applications that may have their
 * own particular ways of reporting errors: log files for a web server,
 * perhaps, and an error dialog for a browser.
 *
 * \todo Do we really need such fine-grained control, or just yes/no tracing? */
void rs_trace_to(rs_trace_fn_t *new_impl)
{
 rs_trace_impl = new_impl;
}

void rs_trace_set_level(rs_loglevel level)
{
 rs_trace_level = level;
}

static void rs_log_va(int flags, char const *fn, char const *fmt, va_list va)
{
 int level = flags & RS_LOG_PRIMASK;

 if (rs_trace_impl && level <= rs_trace_level) {
 char buf[1000];
 char full_buf[1040];

 vsnprintf(buf, sizeof(buf), fmt, va);
 if (flags & RS_LOG_NONAME || !(*fn)) {
 snprintf(full_buf, sizeof(full_buf), "%s: %s%s\n", MY_NAME,
 rs_severities[level], buf);
 } else {
 snprintf(full_buf, sizeof(full_buf), "%s: %s(%s) %s\n", MY_NAME,
 rs_severities[level], fn, buf);
 }
 rs_trace_impl(level, full_buf);
 }
}

/* Called by a macro that prepends the calling function name, etc. */
void rs_log0(int level, char const *fn, char const *fmt, ...)
{
 va_list va;

 va_start(va, fmt);
 rs_log_va(level, fn, fmt, va);
 va_end(va);
}

void rs_trace_stderr(rs_loglevel UNUSED(level), char const *msg)
{
 fputs(msg, stderr);
}

int rs_supports_trace(void)
{
#ifdef DO_RS_TRACE
 return 1;
#else
 return 0;
#endif /* !DO_RS_TRACE */
}
```

--------------------------------

### Configure CMake with options

Source: https://librsync.github.io/page_install.html

Use this command to pass custom options to CMake during the configure step.

```bash
$ cmake -D <option-name>=<value> .

```