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Struct N_STR Struct N_TIFF Struct N_TIFF_ENTRY Struct N_TIME Struct N_URL Struct N_URL_PARAM Struct N_USER Struct N_USERLIST Struct N_WS_CONN Struct N_WS_FRAME Struct N_WS_MESSAGE Struct N_ZIP_MEMBER Struct OCTREE Struct OCTREE_NODE Struct PARSER Struct PARTICLE Struct PARTICLE_EMITTER Struct PARTICLE_SYSTEM Struct PEER Struct PHYSICS Struct PK_OBJ Struct PK_VM Struct POINT2D Struct POINT3D Struct PRETTY_OUT Struct QNODE Struct QUADTREE Struct QUADTREE_NODE Struct REC Struct RGB Struct SAMPLE Struct SEEN Struct SHARER Struct SRV Struct SRV_ARG Struct STACK Struct STACK_ITEM Struct SYNTAX_RUN Struct THREAD_POOL Struct THREAD_POOL_NODE Struct THREAD_WAITING_PROC Struct TRAJECTORY Struct TRAJECTORY_POINT Struct TREE Struct TREE_NODE Struct TS_LOG Struct WAYPOINT3D Struct WORKER_ARG Struct ZIP_SINK Struct _N_DC_ENTRY Struct _N_DC_GROUP_ENTRY Struct _N_GUI_COLORWHEEL Struct _N_GUI_COLORWHEEL_BLOCK Struct _N_GUI_COLORWHEEL_MOUSE Struct _N_GUI_CURVE Struct _N_GUI_CURVE_BLOCK Struct _N_GUI_CURVE_MOUSE Struct _N_GUI_GRID Struct _N_GUI_POPUP_ENTRY Struct _N_GUI_POPUP_LEVEL Struct _N_GUI_SB_SKIN Struct _N_GUI_TA_STEP Struct _N_GUI_THUMB Struct _N_GUI_WRAP_ACC Struct _compiled Struct _conn Struct _ip_slot Struct _mp_param Struct _n_civil Struct _seg Struct client Struct collector Struct date_vector Struct md_atom Struct md_cells Struct md_hit Struct md_line_ctx Struct mline Struct n_http_req_header Struct n_http_req_limits Struct n_http_request Struct n_markdown_block Struct n_markdown_doc Struct n_markdown_inline Struct n_markdown_span Struct n_reactor_stats Struct n_url_safe Struct n_url_safe_head Struct n_wrap_item Struct producer_state Struct rects Struct reply Struct runner Struct sink Struct tbuf Struct wrap_hit Struct wrap_span Structures Union COORD_VALUE Union HASH_DATA Union NODE_DATA_TYPES Union STACK_DATA dir_310dcdd4703e877a6b99d5dc3fc54d27 dir_68267d1309a1af8e8297ef4c3efbcdba dir_d28a4824dc47e487b107a5db32ef43c4 dir_d44c64559bbebec7f509842c48db8b23 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ex_gui_dropmenu_8c example ex_gui_frameless_drag_8c example ex_gui_global_scroll_8c example ex_gui_glyph_8c example ex_gui_grid_8c example ex_gui_hexview_8c example ex_gui_hover_8c example ex_gui_isometric_8c example ex_gui_kvtable_8c example ex_gui_label_fits_8c example ex_gui_label_lines_8c example ex_gui_layout_persist_8c example ex_gui_listbox_8c example ex_gui_md_8c example ex_gui_multiwin_8c example ex_gui_network_8c example ex_gui_particles_8c example ex_gui_placeholder_8c example ex_gui_popup_8c example ex_gui_progressbar_8c example ex_gui_reentrant_8c example ex_gui_round_8c example ex_gui_sectionlist_8c example ex_gui_slider_default_8c example ex_gui_slider_handle_8c example ex_gui_slider_step_8c example ex_gui_splitpane_8c example ex_gui_suggest_8c example ex_gui_syntaxview_8c example ex_gui_text_shorten_8c example ex_gui_textarea_selection_8c example ex_gui_tooltip_8c example ex_gui_tree_lazy_8c example ex_gui_tree_order_8c example ex_gui_tree_state_8c example ex_gui_window_rect_8c example ex_gui_zorder_8c example ex_hash_8c example ex_hex_8c example ex_html_8c example ex_http2_8c example ex_http2_server_8c example ex_http_cookie_8c example ex_http_form_8c example ex_http_mime_8c example ex_http_req_8c example ex_http_response_8c example ex_http_router_8c example ex_http_server_8c example ex_icc_8c example ex_iso_astar_8c example ex_json_8c example ex_kafka_8c example ex_linalg_8c example ex_list_8c example ex_log_8c example ex_markdown_8c example ex_module_8c example ex_monolith_8c example ex_network_8c example ex_network_8h example ex_network_accept_8c example ex_network_alpn_8c example ex_network_connect_abort_8c example ex_network_mock_8c example ex_network_proxy_8c example ex_network_reactor_8c example ex_network_sni_8c example ex_network_sse_8c example ex_network_ssl_8c example ex_network_ssl_hardened_8c example ex_network_ssl_hostname_8c example ex_network_ssl_nonblock_8c example ex_network_tls_defaults_8c example ex_network_ws_8c example ex_network_ws_limits_8c example ex_nstr_8c example ex_parallel_for_8c example ex_parallel_team_8c example ex_pcre_8c example ex_pretty_8c example ex_pth_8c example ex_query_8c example ex_random_8c example ex_sha256_8c example ex_signals_8c example ex_spawn_8c example ex_ssrf_8c example ex_stack_8c example ex_threads_8c example ex_tiff_8c example ex_time_formats_8c example ex_trajectory_8c example ex_trees_8c example ex_url_8c example ex_url_safe_8c example ex_wrap_8c example ex_x509_8c example ex_zip_8c example ex_zlib_8c example mainpage_8dox n__3d_8c n__3d_8h n__aabb_8c n__aabb_8h n__allegro5_8c n__allegro5_8h n__allegro__4_8c n__allegro__4_8h n__anim_8c n__anim_8h n__astar_8c n__astar_8h n__atlas_8c n__atlas_8h n__avro_8c n__avro_8h n__base64_8c n__base64_8h n__clipboard_8c n__clipboard_8h n__clock__sync_8c n__clock__sync_8h n__common_8c n__common_8h n__config__file_8c n__config__file_8h n__cookies_8c n__cookies_8h n__crypto_8c n__crypto_8h n__dead__reckoning_8c 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5 Module N_ENTROPY
gullradriel edited this page 2026-10-09 00:55:18 +02:00
Table of Contents

ENTROPY: randomness metrics for byte samples

Structures

Name
struct N_ENTROPY_POS
per-position statistics across a set of equal-length samples
struct N_ENTROPY_BIT
per-bit statistics across a set of equal-length samples

Functions

Name
double n_entropy_shannon(const unsigned char * data, size_t len)
Shannon entropy of the byte sample, in bits per byte (0.0 .
double n_entropy_runs_p(const unsigned char * data, size_t len)
Runs test over the sample's bit stream (NIST SP 800-22 style).
size_t n_entropy_positions(const unsigned char *const * samples, size_t count, size_t sample_len, N_ENTROPY_POS * out, size_t max_out)
Per-POSITION analysis of a set of equal-length samples.
double n_entropy_monobit(const unsigned char * data, size_t len)
Fraction of set bits in the sample (0.0 .
size_t n_entropy_longest_run(const unsigned char * data, size_t len)
Length of the longest run of identical bits in the sample.
double n_entropy_chi_square_p(double chi, size_t df)
Upper-tail p-value of a chi-square statistic (Wilson-Hilferty).
double n_entropy_chi_square(const unsigned char * data, size_t len)
Chi-square statistic of the byte histogram against a uniform distribution over 256 values.
size_t n_entropy_bits(const unsigned char *const * samples, size_t count, size_t sample_len, N_ENTROPY_BIT * out, size_t max_out)
Per-BIT analysis of a set of equal-length samples.

Functions Documentation

function n_entropy_shannon

double n_entropy_shannon(
    const unsigned char * data,
    size_t len
)

Shannon entropy of the byte sample, in bits per byte (0.0 .

. 8.0). 0 means a single repeated value; 8 means a perfectly uniform byte histogram. Returns 0.0 for an empty/NULL sample.

function n_entropy_runs_p

double n_entropy_runs_p(
    const unsigned char * data,
    size_t len
)

Runs test over the sample's bit stream (NIST SP 800-22 style).

Counts the transitions between runs of equal bits and scores them against what a fair coin would produce. It catches what monobit cannot: a stream with exactly half its bits set but arranged as 0000...1111 passes monobit and fails this. Returns the two-sided p-value (near 1.0 is unremarkable), or 0.0 when the sample is empty or its monobit fraction is too skewed for the test to apply.

function n_entropy_positions

size_t n_entropy_positions(
    const unsigned char *const * samples,
    size_t count,
    size_t sample_len,
    N_ENTROPY_POS * out,
    size_t max_out
)

Per-POSITION analysis of a set of equal-length samples.

Parameters:

  • samples array of count pointers, each to sample_len bytes
  • count number of samples (positions need several to mean anything)
  • sample_len length of every sample
  • out array receiving one entry per position
  • max_out capacity of out

Return: the number of positions written, or 0 on a bad argument

An aggregate metric over concatenated tokens hides the finding that matters: a token can look random overall while its third character is always one of two values, or its counter half increments. This reports each byte position separately, so the caller can name WHICH position is predictable.

function n_entropy_monobit

double n_entropy_monobit(
    const unsigned char * data,
    size_t len
)

Fraction of set bits in the sample (0.0 .

. 1.0); 0.5 is the ideal for random data (the FIPS monobit idea). Returns 0.0 for an empty/NULL sample.

function n_entropy_longest_run

size_t n_entropy_longest_run(
    const unsigned char * data,
    size_t len
)

Length of the longest run of identical bits in the sample.

A long run in a token set is a stuck field; returns 0 for an empty sample.

function n_entropy_chi_square_p

double n_entropy_chi_square_p(
    double chi,
    size_t df
)

Upper-tail p-value of a chi-square statistic (Wilson-Hilferty).

How surprising chi is for df degrees of freedom if the data really were uniform: near 1.0 means unremarkable, near 0.0 means the distribution is skewed far beyond chance. The Wilson-Hilferty cube-root transform is used rather than the exact incomplete gamma: it is accurate to a few thousandths for df >= 3, which is well inside what a verdict needs, and it is a dozen lines instead of a numerics library. Returns 1.0 for df == 0 or a non-positive statistic.

function n_entropy_chi_square

double n_entropy_chi_square(
    const unsigned char * data,
    size_t len
)

Chi-square statistic of the byte histogram against a uniform distribution over 256 values.

Near 255 (the degrees of freedom) for random data; large for skewed data. Returns 0.0 for an empty/NULL sample.

function n_entropy_bits

size_t n_entropy_bits(
    const unsigned char *const * samples,
    size_t count,
    size_t sample_len,
    N_ENTROPY_BIT * out,
    size_t max_out
)

Per-BIT analysis of a set of equal-length samples.

Parameters:

  • samples array of count pointers, each to sample_len bytes
  • count number of samples
  • sample_len length of every sample
  • out array receiving one entry per bit (sample_len * 8 of them)
  • max_out capacity of out

Return: the number of bits written, or 0 on a bad argument

The bit-level counterpart of n_entropy_positions: it finds a bit that is stuck, or biased, across the sample set, which is how a truncated counter or a fixed-prefix identifier shows up.

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