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#include "../defs/all.h"
#include "../defs/widechar.h"
/* this reads one utf81 character from the start of bytes
it puts the character's number in *codepoint and returns how many bytes it used (its always 1 or more)
invalid input it stores U+FFFD (�) and returns 1, so the caller always moves forward. */
int utf8_decode(const unsigned char *bytes, unsigned long *codepoint){
unsigned long value = bytes[0];
unsigned long minallowed = 0; //rejects overlong encodings
int sequence_length;
int byte_index;
if(value < 0x80){
*codepoint = value;
return 1;
} else if(value >= 0xC2 && value <= 0xDF){
sequence_length = 2;
value &= 0x1F;
minallowed = 0x80;
} else if(value >= 0xE0 && value <= 0xEF){
sequence_length = 3;
value &= 0x0F;
minallowed = 0x800;
} else if(value >= 0xF0 && value <= 0xF4){
sequence_length = 4;
value &= 0x07;
minallowed = 0x10000;
} else {
*codepoint = 0xFFFD;
return 1;
}
for(byte_index = 1; byte_index < sequence_length; byte_index++){
if((bytes[byte_index] & 0xC0) != 0x80){
*codepoint = 0xFFFD;
return 1;
}
value = (value << 6) | (bytes[byte_index] & 0x3F);
}
if(value < minallowed || value > 0x10FFFF || (value >= 0xD800 && value <= 0xDFFF)){
*codepoint = 0xFFFD;
return 1;
}
*codepoint = value;
return sequence_length;
}
/* this turns the library's return value into a column count so 0 1 or 2 */
static int codepoint_width(unsigned long codepoint){
int width = widechar_wcwidth(codepoint);
if(width > 0)
return width;
switch(width){
case widechar_ambiguous:
case widechar_private_use:
return 1;
case widechar_widened_in_9:
return 2;
default:
return 0;
}
}
/* how many terminal columns a string takes up */
int displaywidth(const char *text){
const unsigned char *current_byte = (const unsigned char *)text;
int total_width = 0;
while(*current_byte){
unsigned long codepoint;
current_byte += utf8_decode(current_byte, &codepoint);
total_width += codepoint_width(codepoint);
}
return total_width;
}
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