From: porkchop@invalid.foo
On Fri, 12 Dec 2025 15:33:01 -0800, Chris M. Thomasson wrote:
> define the probability? Say in 0...1?
Probabilities for Chris... Enjoy.
#include
#include
#include
/*
* map_strict[]
*
* Valid bytes:
* - ASCII printable: 0x20–0x7E
* - ISO-8859-1 high printable: 0xA0–0xFF
* - Whitespace: TAB (0x09), LF (0x0A), CR (0x0D)
*
* Invalid bytes (binary indicators):
* - NULL byte (0x00)
* - C0 controls (0x01–0x08, 0x0B–0x0C, 0x0E–0x1F)
* - DEL (0x7F)
* - C1 controls (0x80–0x9F)
*/
static const uint8_t map_strict[256] = {
0,0,0,0,0,0,0,0,0,1,1,0,0,1,0,0, // 00
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 10
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 20
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 30
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 40
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 50
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 60
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0, // 70
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 80
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 90
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // A0
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // B0
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // C0
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // D0
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // E0
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1 // F0
};
/*
* map_loose[]
*
* Valid bytes:
* - ASCII printable characters: 0x20–0x7E
* - Whitespace: TAB (0x09), LF (0x0A), CR (0x0D)
* - High bytes: 0x80–0xFF
*
* Invalid bytes (binary indicators):
* - NULL byte: 0x00
* - C0 control codes: 0x01–0x08, 0x0B–0x0C, 0x0E–0x1F
* - DEL character: 0x7F
*/
static const uint8_t map_loose[256] = {
0,0,0,0,0,0,0,0,0,1,1,0,0,1,0,0, // 00
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 10
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 20
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 30
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 40
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 50
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 60
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 70
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 80
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 90
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // A0
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // B0
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // C0
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // D0
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // E0
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1 // F0
};
/*
* is_text_file(const char *path, const uint8_t map[256], double probability)
*
* Determines whether a file is likely a text file driven by a byte map
* & probability threshold.
*
* Signature:
*
* path
* Pathname of the file to examine. The function follows symlinks
* & only operates on regular files.
*
* map[256]
* A 256-entry lookup table indexed by byte value (0–255).
* Each entry must be either:
* 1 -> byte is considered valid text
* 0 -> byte is considered invalid (binary indicator)
*
* probability
* Maximum allowed percentage (0.0 to 100.0) of invalid bytes.
* If the percentage of bytes for which map[byte] == 0 exceeds
* this value, the file is classified as non-text.
*
* Behavior:
* - Reads the file in binary mode.
* - Counts total bytes & 'bad' bytes (map[] == 0).
* - Returns 1 if bad byte percentage <= probability.
* - Returns 0 if bad byte percentage > probability.
* - Returns -1 on access/open errors or if the file is not regular.
* - Function exits early if impossible to satisfy probability threshold.
*
* Returns:
* 1 - text
* 0 - binary indicator
* -1 - could not open
*
* Example with 94.3% probability threshold:
* is_text_file("./example.txt", your_map[256], 94.3)
*
*/
int is_text_file(const char *path, const uint8_t map[256], double probability)
{
struct stat st;
if (stat(path, &st) != 0) return -1; // can not access file
if (!S_ISREG(st.st_mode)) return -1; // reject: directories/devices/sockets
FILE *f = fopen(path, "rb"); if (!f) return -1; // could not open file
// 4KB: 4096, 8KB: 8192, 16KB: 16384, 32KB: 32768, 64KB: 65536
unsigned char buf[16384];
size_t n, i;
size_t total = 0;
size_t bad = 0;
while ((n = fread(buf, 1, sizeof(buf), f)) > 0) {
for (i = 0; i < n; i++) {
total++;
if (!map[buf[i]]) bad++;
if (((double)bad / total) * 100.0 > probability) {
fclose(f);
return 0; // not text
}
}
}
fclose(f);
if (total == 0) return 0; // empty file or total binary...
// final probability check
return (((double)bad / total) * 100.0 <= probability) ? 1 : 0;
}
--
:wq
Mike Sanders
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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