c - Map variable-length string to int -
i can't figure out how write function takes following input , produces following output:
in (int) | out (char *) 0 | "" 1 | "a" 2 | "b" 3 | "c" 4 | "aa" 5 | "ab" 6 | "ac" 7 | "ba" 8 | "bb" ... it not converting input ternary, there difference "a" , "aa" (whereas there no difference between 0 , 00).
i have found correlation between length of string , input (len = floor(log2(in + 1)), when use a , b:
in (int) | floor(log2(in + 1)) | out (char *) 0 | 0 | "" 1 | 1 | "a" 2 | 1 | "b" 3 | 2 | "aa" 4 | 2 | "ab" 5 | 2 | "ba" 6 | 2 | "bb" 7 | 3 | "aaa" 8 | 3 | "aab" what's general correlation between length of output , input value, given there n different valid characters?
this related to, distinctly different from, calc cell convertor in c. code swiftly derived code:
#include <ctype.h> #include <stdio.h> #include <string.h> /* these declarations should in header */ extern char *b3_row_encode(unsigned row, char *buffer); extern unsigned b3_row_decode(const char *buffer); static char *b3_encode(unsigned row, char *buffer) { unsigned div = row / 3; unsigned rem = row % 3; if (div > 0) buffer = b3_encode(div-1, buffer); *buffer++ = rem + 'a'; *buffer = '\0'; return buffer; } char *b3_row_encode(unsigned row, char *buffer) { if (row == 0) { *buffer = '\0'; return buffer; } return(b3_encode(row-1, buffer)); } unsigned b3_row_decode(const char *code) { unsigned char c; unsigned r = 0; while ((c = *code++) != '\0') { if (!isalpha(c)) break; c = tolower(c); r = r * 3 + c - 'a' + 1; } return r; } #ifdef test static const struct { unsigned col; char cell[10]; } tests[] = { { 0, "" }, { 1, "a" }, { 2, "b" }, { 3, "c" }, { 4, "aa" }, { 5, "ab" }, { 6, "ac" }, { 7, "ba" }, { 8, "bb" }, { 9, "bc" }, { 10, "ca" }, { 11, "cb" }, { 12, "cc" }, { 13, "aaa" }, { 14, "aab" }, { 16, "aba" }, { 22, "baa" }, { 169, "abcba" }, }; enum { num_tests = sizeof(tests) / sizeof(tests[0]) }; int main(void) { int pass = 0; (int = 0; < num_tests; i++) { char buffer[32]; b3_row_encode(tests[i].col, buffer); unsigned n = b3_row_decode(buffer); const char *pf = "fail"; if (strcmp(tests[i].cell, buffer) == 0 && n == tests[i].col) { pf = "pass"; pass++; } printf("%s: col %3u, cell (wanted: %-8s vs actual: %-8s) col = %3u\n", pf, tests[i].col, tests[i].cell, buffer, n); } if (pass == num_tests) printf("== pass == %d tests ok\n", pass); else printf("!! fail !! %d out of %d failed\n", (num_tests - pass), num_tests); return (pass == num_tests) ? 0 : 1; } #endif /* test */ the code includes test program , function convert string integer , function convert integer string. tests run back-to-back conversions. code not handle empty string zero.
sample output:
pass: col 0, cell (wanted: vs actual: ) col = 0 pass: col 1, cell (wanted: vs actual: ) col = 1 pass: col 2, cell (wanted: b vs actual: b ) col = 2 pass: col 3, cell (wanted: c vs actual: c ) col = 3 pass: col 4, cell (wanted: aa vs actual: aa ) col = 4 pass: col 5, cell (wanted: ab vs actual: ab ) col = 5 pass: col 6, cell (wanted: ac vs actual: ac ) col = 6 pass: col 7, cell (wanted: ba vs actual: ba ) col = 7 pass: col 8, cell (wanted: bb vs actual: bb ) col = 8 pass: col 9, cell (wanted: bc vs actual: bc ) col = 9 pass: col 10, cell (wanted: ca vs actual: ca ) col = 10 pass: col 11, cell (wanted: cb vs actual: cb ) col = 11 pass: col 12, cell (wanted: cc vs actual: cc ) col = 12 pass: col 13, cell (wanted: aaa vs actual: aaa ) col = 13 pass: col 14, cell (wanted: aab vs actual: aab ) col = 14 pass: col 16, cell (wanted: aba vs actual: aba ) col = 16 pass: col 22, cell (wanted: baa vs actual: baa ) col = 22 pass: col 169, cell (wanted: abcba vs actual: abcba ) col = 169 == pass == 18 tests ok
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