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libc: add encode(2) variants for custom alphabets

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There are a number of alphabets in common use for base32
and base64 encoding, such as url-safe encodings.

This adds support for passing a function to encode into
arbitary alphabets.
This commit is contained in:
Ori Bernstein 2021-07-03 20:03:17 +00:00
parent c848ca6267
commit e934530ee4
4 changed files with 99 additions and 31 deletions
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6
sys/include/libc.h
View file

@ -385,10 +385,15 @@ extern double charstod(int(*)(void*), void*);
extern char* cleanname(char*);
extern int decrypt(void*, void*, int);
extern int encrypt(void*, void*, int);
extern int dec64(uchar*, int, char*, int);
extern int enc64(char*, int, uchar*, int);
extern int dec64x(uchar*, int, char*, int, int (*)(int));
extern int enc64x(char*, int, uchar*, int, int (*)(int));
extern int dec32(uchar*, int, char*, int);
extern int enc32(char*, int, uchar*, int);
extern int dec32x(uchar*, int, char*, int, int (*)(int));
extern int enc32x(char*, int, uchar*, int, int (*)(int));
extern int dec16(uchar*, int, char*, int);
extern int enc16(char*, int, uchar*, int);
extern int dec64chr(int);
@ -397,6 +402,7 @@ extern int dec32chr(int);
extern int enc32chr(int);
extern int dec16chr(int);
extern int enc16chr(int);
extern int encodefmt(Fmt*);
extern void exits(char*);
extern double frexp(double, int*);

38
sys/man/2/encode
View file

@ -1,6 +1,7 @@
.TH ENCODE 2
.SH NAME
dec64, enc64, dec32, enc32, dec16, enc16, \
dec64x, enc64x, dec32x, enc32x, \
dec64chr, enc64chr, dec32chr, enc32chr, dec16chr, enc16chr, \
encodefmt \- encoding byte arrays as strings
.SH SYNOPSIS
@ -12,15 +13,27 @@ encodefmt \- encoding byte arrays as strings
int dec64(uchar *out, int lim, char *in, int n)
.PP
.B
int dec64x(uchar *out, int lim, char *in, int n, int (*map)(int))
.PP
.B
int enc64(char *out, int lim, uchar *in, int n)
.PP
.B
int enc64x(char *out, int lim, uchar *in, int n, int (*map)(int))
.PP
.B
int dec32(uchar *out, int lim, char *in, int n)
.PP
.B
int dec32x(uchar *out, int lim, char *in, int n, int (*map)(int))
.PP
.B
int enc32(char *out, int lim, uchar *in, int n)
.PP
.B
int enc32x(char *out, int lim, uchar *in, int n, int (*map)(int))
.PP
.B
int dec16(uchar *out, int lim, char *in, int n)
.PP
.B
@ -82,6 +95,31 @@ and
.I enc64chr
encode a symbol of the alphabet given a value.
if the value is out of range then zero is returned.
.PP
The
.I enc64x
and
.I enc32x
variants are identical to the above, except that they take a
function mapping from an arbitrary index in the alphabet to
the encoded character.
For example, in the following 32-character alphabet,
.EX
.I ABCDEFGHIJKLMNOPQRSTUVWXYZ234567
.EE
the chr function would map the value
.I 3
to the character
.IR D .
The
.I dec64x
and
.I dec32x
variants are similar to the above, however the function passed
maps from a character within the alphabet to the index within
the alphabet.
.PP
.I Encodefmt
can be used with

50
sys/src/libc/port/u32.c
View file

@ -25,7 +25,7 @@ dec32chr(int c)
}
int
dec32(uchar *dest, int ndest, char *src, int nsrc)
dec32x(uchar *dest, int ndest, char *src, int nsrc, int (*chr)(int))
{
uchar *start;
int i, j, u[8];
@ -35,7 +35,7 @@ dec32(uchar *dest, int ndest, char *src, int nsrc)
start = dest;
while(nsrc>=8){
for(i=0; i<8; i++){
j = dec32chr(src[i]);
j = chr(src[i]);
if(j < 0)
j = 0;
u[i] = j;
@ -52,7 +52,7 @@ dec32(uchar *dest, int ndest, char *src, int nsrc)
if(nsrc == 1 || nsrc == 3 || nsrc == 6)
return -1;
for(i=0; i<nsrc; i++){
j = dec32chr(src[i]);
j = chr(src[i]);
if(j < 0)
j = 0;
u[i] = j;
@ -73,7 +73,7 @@ out:
}
int
enc32(char *dest, int ndest, uchar *src, int nsrc)
enc32x(char *dest, int ndest, uchar *src, int nsrc, int (*chr)(int))
{
char *start;
int j;
@ -83,50 +83,62 @@ enc32(char *dest, int ndest, uchar *src, int nsrc)
start = dest;
while(nsrc>=5){
j = (0x1f & (src[0]>>3));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x1c & (src[0]<<2)) | (0x03 & (src[1]>>6));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x1f & (src[1]>>1));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x10 & (src[1]<<4)) | (0x0f & (src[2]>>4));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x1e & (src[2]<<1)) | (0x01 & (src[3]>>7));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x1f & (src[3]>>2));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x18 & (src[3]<<3)) | (0x07 & (src[4]>>5));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x1f & (src[4]));
*dest++ = enc32chr(j);
*dest++ = chr(j);
src += 5;
nsrc -= 5;
}
if(nsrc){
j = (0x1f & (src[0]>>3));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x1c & (src[0]<<2));
if(nsrc == 1)
goto out;
j |= (0x03 & (src[1]>>6));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x1f & (src[1]>>1));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x10 & (src[1]<<4));
if(nsrc == 2)
goto out;
j |= (0x0f & (src[2]>>4));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x1e & (src[2]<<1));
if(nsrc == 3)
goto out;
j |= (0x01 & (src[3]>>7));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x1f & (src[3]>>2));
*dest++ = enc32chr(j);
*dest++ = chr(j);
j = (0x18 & (src[3]<<3));
out:
*dest++ = enc32chr(j);
*dest++ = chr(j);
}
*dest = 0;
return dest-start;
}
int
enc32(char *dest, int ndest, uchar *src, int nsrc)
{
return enc32x(dest, ndest, src, nsrc, enc32chr);
}
int
dec32(uchar *dest, int ndest, char *src, int nsrc)
{
return dec32x(dest, ndest, src, nsrc, dec32chr);
}

36
sys/src/libc/port/u64.c
View file

@ -30,7 +30,7 @@ dec64chr(int c)
}
int
dec64(uchar *out, int lim, char *in, int n)
dec64x(uchar *out, int lim, char *in, int n, int (*chr)(int))
{
ulong b24;
uchar *start = out;
@ -40,7 +40,7 @@ dec64(uchar *out, int lim, char *in, int n)
b24 = 0;
i = 0;
while(n-- > 0){
c = dec64chr(*in++);
c = chr(*in++);
if(c < 0)
continue;
switch(i){
@ -84,7 +84,7 @@ exhausted:
}
int
enc64(char *out, int lim, uchar *in, int n)
enc64x(char *out, int lim, uchar *in, int n, int (*chr)(int))
{
int i;
ulong b24;
@ -97,10 +97,10 @@ enc64(char *out, int lim, uchar *in, int n)
b24 |= *in++;
if(out + 4 >= e)
goto exhausted;
*out++ = enc64chr(b24>>18);
*out++ = enc64chr((b24>>12)&0x3f);
*out++ = enc64chr((b24>>6)&0x3f);
*out++ = enc64chr(b24&0x3f);
*out++ = chr(b24>>18);
*out++ = chr((b24>>12)&0x3f);
*out++ = chr((b24>>6)&0x3f);
*out++ = chr(b24&0x3f);
}
switch(n%3){
@ -109,17 +109,17 @@ enc64(char *out, int lim, uchar *in, int n)
b24 |= *in<<8;
if(out + 4 >= e)
goto exhausted;
*out++ = enc64chr(b24>>18);
*out++ = enc64chr((b24>>12)&0x3f);
*out++ = enc64chr((b24>>6)&0x3f);
*out++ = chr(b24>>18);
*out++ = chr((b24>>12)&0x3f);
*out++ = chr((b24>>6)&0x3f);
*out++ = '=';
break;
case 1:
b24 = *in<<16;
if(out + 4 >= e)
goto exhausted;
*out++ = enc64chr(b24>>18);
*out++ = enc64chr((b24>>12)&0x3f);
*out++ = chr(b24>>18);
*out++ = chr((b24>>12)&0x3f);
*out++ = '=';
*out++ = '=';
break;
@ -128,3 +128,15 @@ exhausted:
*out = 0;
return out - start;
}
int
enc64(char *out, int lim, uchar *in, int n)
{
return enc64x(out, lim, in, n, enc64chr);
}
int
dec64(uchar *out, int lim, char *in, int n)
{
return dec64x(out, lim, in, n, dec64chr);
}