Trimming and Translating

Allocates and reuses tape like sz_strings_to_tape_best. The mapping keeps every length, so a span over the caller's own buffers of matching sizes needs no allocator, and a span that strings views is mapped in place.

Can be used to implement some form of string normalization, partially masking punctuation marks, or converting between different character sets, like uppercase or lowercase. Surprisingly, also has broad implications in image processing, where channel transformations often use LUTs.

Lowercasing a buffer in place, as a tape of one string:

#include <ctype.h> // for tolower
#include <stringzilla/strings.h>
int main() {
     sz_capability_t capabilities;
     char to_lower_lut[256];
     for (int i = 0; i < 256; ++i) to_lower_lut[i] = tolower(i);
     char buffer[3] = {'A', 'B', 'C'};
     sz_u32_t offsets[2] = {0, 3};
     sz_strings_span_t tape;
     tape.layout = sz_strings_u32_tape_k, tape.count = 1;
     tape.data.u32_tape.data = buffer, tape.data.u32_tape.offsets = offsets;
     sz_strings_view_t strings;
     sz_strings_from_span(&tape, &strings);
     sz_capabilities_enabled_cpu(&capabilities);
     sz_strings_lookup_best(&strings, NULL, 1, to_lower_lut, NULL, &tape, capabilities, NULL);
     return buffer[0] == 'a' && buffer[1] == 'b' && buffer[2] == 'c' ? 0 : 1;
}

ASCII characters [A, Z] map to decimals [65, 90], and [a, z] map to [97, 122]. So there are 26 English letters, shifted by 32 values, meaning that a conversion can be done by flipping the 5th bit of each inappropriate character byte. This, however, breaks for extended ASCII, so a different solution is needed.

ASCII characters [A, Z] map to decimals [65, 90], and [a, z] map to [97, 122]. So there are 26 English letters, shifted by 32 values, meaning that a conversion can be done by flipping the 5th bit of each inappropriate character byte. This, however, breaks for extended ASCII, so a different solution is needed.