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#include "fmt.h"
size_t scan_utf8(const char* in,size_t len,uint32_t* num) {
uint32_t i,k,m;
const char* orig=in;
if (len==0) return 0;
i=(*(unsigned char*)in++); /* grab first byte */
if (i>=0xfe || /* 0xfe and 0xff are invalid encodings in utf-8 for the first byte */
(i&0xc0)==0x80) return 0; /* first bits being 10 marks continuation chars, invalid sequence for first byte */
for (k=0; i&0x80; i<<=1, ++k); /* count leading 1 bits */
if (!k) {
if (num) *num=i;
return 1;
}
if (k>len) return 0;
i=(i&0xff)>>k; /* mask the leading 1 bits */
/* The next part is a little tricky.
* UTF-8 says that the encoder has to choose the most efficient
* encoding, and the decoder has to reject other encodings. The
* background is that attackers encoded '/' not as 0x2f but as 0xc0
* 0xaf, and that evaded bad security checks just scan for the '/'
* byte in pathnames.
* At this point k contains the number of bytes, so k-1 is the number
* of continuation bytes. For each additional continuation byte, we
* gain 6 bits of storage space, but we lose one in the signalling in
* the initial byte. So we have 6 + (k-1) * 5 bits total storage
* space for this encoding. The minimum value for k bytes is the
* maximum number for k-1 bytes plus 1. If the previous encoding has
* 11 bits, its maximum value is 11 1-bits or 0x7ff, and the minimum
* value we are looking for is 0x800 or 1<<11. For 2 bytes, UTF-8 can
* encode 11 bits, after that each additional byte gains 5 more bits.
* So for k>2, we want
* 1 << (11+(k-3)*5)
* or optimized to get rid of the -3
* 1 << (k*5-4)
* but for k==2 the delta is 4 bits (not 5), so we want
* 1 << 7
* abusing the fact that a boolean expression evaluates to 0 or 1, the
* expression can be written as
* 1 << (k*5-4+(k==2))
*/
m=((uint32_t)1<<(k*5-4+(k==2)));
while (k>1) {
if ((*in&0xc0)!=0x80) return 0;
i=(i<<6) | ((*in++)&0x3f);
--k;
}
if (i<m) return 0; /* if the encoded value was less than m, reject */
if (num) *num=i;
return (size_t)(in-orig);
}
#ifdef UNITTEST
#include <assert.h>
#include "fmt/fmt_utf8.c"
int main() {
char buf[100];
uint32_t l;
unsigned int i;
/* first positive testing for the various lengths */
l=fmt_utf8(buf,0); assert(l == 1 && scan_utf8(buf,l+1,&l)==1 && l==0);
l=fmt_utf8(buf,0x80); assert(l == 2 && scan_utf8(buf,l+1,&l)==2 && l==0x80);
l=fmt_utf8(buf,0x800); assert(l == 3 && scan_utf8(buf,l+1,&l)==3 && l==0x800);
l=fmt_utf8(buf,0x10000); assert(l == 4 && scan_utf8(buf,l+1,&l)==4 && l==0x10000);
l=fmt_utf8(buf,0x200000); assert(l == 5 && scan_utf8(buf,l+1,&l)==5 && l==0x200000);
l=fmt_utf8(buf,0x4000000); assert(l == 6 && scan_utf8(buf,l+1,&l)==6 && l==0x4000000);
/* corner cases */
l=fmt_utf8(buf,0x7f); assert(l == 1 && scan_utf8(buf,l+1,&l)==1 && l==0x7f);
l=fmt_utf8(buf,0x7ff); assert(l == 2 && scan_utf8(buf,l+1,&l)==2 && l==0x7ff);
l=fmt_utf8(buf,0xffff); assert(l == 3 && scan_utf8(buf,l+1,&l)==3 && l==0xffff);
l=fmt_utf8(buf,0x1fffff); assert(l == 4 && scan_utf8(buf,l+1,&l)==4 && l==0x1fffff);
l=fmt_utf8(buf,0x3ffffff); assert(l == 5 && scan_utf8(buf,l+1,&l)==5 && l==0x3ffffff);
l=fmt_utf8(buf,0x7fffffff); assert(l == 6 && scan_utf8(buf,l+1,&l)==6 && l==0x7fffffff);
/* more corner cases */
l=fmt_utf8(buf,0xd7ff); assert(l == 3 && scan_utf8(buf,l+1,&l)==3 && l==0xd7ff);
l=fmt_utf8(buf,0xe000); assert(l == 3 && scan_utf8(buf,l+1,&l)==3 && l==0xe000);
l=fmt_utf8(buf,0xfffd); assert(l == 3 && scan_utf8(buf,l+1,&l)==3 && l==0xfffd);
l=fmt_utf8(buf,0x10ffff); assert(l == 4 && scan_utf8(buf,l+1,&l)==4 && l==0x10ffff);
l=fmt_utf8(buf,0x110000); assert(l == 4 && scan_utf8(buf,l+1,&l)==4 && l==0x110000);
/* now negative testing */
/* start off with some continuation bytes outside a sequence */
for (i=0x80; i<=0xbf; ++i) {
buf[0]=i;
assert(scan_utf8(buf,2,&l)==0);
}
/* now check lonely sequence start characters */
buf[1]=' ';
for (i=0xc0; i<=0xfd; ++i) {
buf[0]=i;
assert(scan_utf8(buf,2,&l)==0);
}
/* FE and FF are reserved for UTF-16 endianness detection*/
assert(scan_utf8("\xfe\xff",3,&l)==0);
assert(scan_utf8("\xff\xfe",3,&l)==0);
/* now check some truncated sequences */
l=fmt_utf8(buf,0); assert(l == 1 && scan_utf8(buf,l-1,&l)==0);
l=fmt_utf8(buf,0x80); assert(l == 2 && scan_utf8(buf,l-1,&l)==0);
l=fmt_utf8(buf,0x800); assert(l == 3 && scan_utf8(buf,l-1,&l)==0);
l=fmt_utf8(buf,0x10000); assert(l == 4 && scan_utf8(buf,l-1,&l)==0);
l=fmt_utf8(buf,0x200000); assert(l == 5 && scan_utf8(buf,l-1,&l)==0);
l=fmt_utf8(buf,0x4000000); assert(l == 6 && scan_utf8(buf,l-1,&l)==0);
/* now truncate in another way */
l=fmt_utf8(buf,0x80); buf[l-1]=' '; assert(l == 2 && scan_utf8(buf,l+1,&l)==0);
l=fmt_utf8(buf,0x800); buf[l-1]=' '; assert(l == 3 && scan_utf8(buf,l+1,&l)==0);
l=fmt_utf8(buf,0x10000); buf[l-1]=' '; assert(l == 4 && scan_utf8(buf,l+1,&l)==0);
l=fmt_utf8(buf,0x200000); buf[l-1]=' '; assert(l == 5 && scan_utf8(buf,l+1,&l)==0);
l=fmt_utf8(buf,0x4000000); buf[l-1]=' '; assert(l == 6 && scan_utf8(buf,l+1,&l)==0);
/* now some not minimally encoded utf-8 sequences */
assert(scan_utf8("\xc0\x80",3,&l)==0);
assert(scan_utf8("\xe0\x80\x80",4,&l)==0);
assert(scan_utf8("\xf0\x80\x80\x80",5,&l)==0);
assert(scan_utf8("\xf8\x80\x80\x80\x80",6,&l)==0);
assert(scan_utf8("\xfc\x80\x80\x80\x80\x80",7,&l)==0);
return 0;
}
#endif