OT: RFC, PRNG

well, I lack much better place to ask about this.

for a project of mine, I have needed a fairly special PRNG. the point is to
have a sufficiently large amount of entropy that it generates
hopefully-unique strings.

additionally, it is important that the generated strings are different each
time the app is run, and are different between different installations.

in general, I am using a 4096-bit state.
the state is preserved in files.

the strings are 96-bit numbers encoded in base48 (seemed sane).

there are a few restrictions on name construction:
only letters, numbers, and '_' are allowed;
it is not allowed to have 2 or more '_' chars in a row ("__");
the sequence can't start with a number, and should not start with '_'.

as such, base48 made sense, since:
I only really have enough chars for this;
using only letters, it is always valid;
base52 will not save any chars.


actually, I guess the comment will be if there is any major flaw with this
algo which would limit its ability to produce hopefully unique names (or
anything else worth comment).

special points to anyone who can guess what these names are used for...

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <time.h>

#include <bgbasm.h>

int basm_rand_pos;

/* default initial state: first 1024 digits of PI */

u32 basm_rand_state[128]=
{
0x31415926, 0x53589793, 0x23846264, 0x33832795,
0x02884197, 0x16939937, 0x51058209, 0x74944592,
0x30781640, 0x62862089, 0x98628034, 0x82534211,
0x70679821, 0x48086513, 0x28230664, 0x70938446,

0x09550582, 0x23172535, 0x94081284, 0x81117450,
0x28410270, 0x19385211, 0x05559644, 0x62294895,
0x49303819, 0x64428810, 0x97566593, 0x34461284,
0x75648233, 0x78678316, 0x52712019, 0x09145648,

0x56692346, 0x03486104, 0x54326648, 0x21339360,
0x72602491, 0x41273724, 0x58700660, 0x63155881,
0x74881520, 0x92096282, 0x92540917, 0x15364367,
0x89259036, 0x00113305, 0x30548820, 0x46652138,

0x41469519, 0x41511609, 0x43305727, 0x03657595,
0x91953092, 0x18611738, 0x19326117, 0x93105118,
0x54807446, 0x23799627, 0x49567351, 0x88575272,
0x48912279, 0x38183011, 0x94912983, 0x36733624,

0x40656643, 0x08602139, 0x49463952, 0x24737190,
0x70217986, 0x09437027, 0x70539217, 0x17629317,
0x67523846, 0x74818467, 0x66940513, 0x20005681,
0x27145263, 0x56082778, 0x57713427, 0x57789609,

0x17363717, 0x87214684, 0x40901224, 0x95343014,
0x65495853, 0x71050792, 0x27968925, 0x89235420,
0x19956112, 0x12902196, 0x08640344, 0x18159813,
0x62977477, 0x13099605, 0x18707211, 0x34999999,

0x83729780, 0x49951059, 0x73173281, 0x60963185,
0x95024459, 0x45534690, 0x83026425, 0x22308253,
0x34468503, 0x52619311, 0x88171010, 0x00313783,
0x87528865, 0x87533208, 0x38142061, 0x71776691,

0x47303598, 0x25349042, 0x87554687, 0x31159562,
0x86388235, 0x37875937, 0x51957781, 0x85778053,
0x21712268, 0x06613001, 0x92787661, 0x11959092,
0x16420198, 0x93809525, 0x72010654, 0x85863278
};

static char *basm_base48=
"ABCDEFGHIJKLMNOPQRSTUVWX"
"abcdefghijklmnopqrstuvwx";


void BASM_InitRand()
{
static char buf[256];
FILE *fd;
long long l;
time_t t;
int i, j, k;
u32 i2;

fd=fopen("randbits.txt", "rt");
if(fd)
{
for(i=0; i<16; i++)
{
fgets(buf, 256, fd);
sscanf(buf, "%X %X %X %X %X %X %X %X",
&basm_rand_state[i*8+0],
&basm_rand_state[i*8+1],
&basm_rand_state[i*8+2],
&basm_rand_state[i*8+3],
&basm_rand_state[i*8+4],
&basm_rand_state[i*8+5],
&basm_rand_state[i*8+6],
&basm_rand_state[i*8+7]);
}
fclose(fd);
}

t=time(NULL);

l=*(u32 *)(&t);
for(i=0; i<128; i++)
{
l=l*65521+basm_rand_state[i];
basm_rand_state[i]=(l>>16)&0xFFFFFFFF;
}
basm_rand_state[0]^=(u32)l;

fd=fopen("randbits.txt", "wt");
if(fd)
{
for(i=0; i<16; i++)
{
for(j=0; j<8; j++)
fprintf(fd, "%08X ", basm_rand_state[i*8+j]);
fprintf(fd, "\n");
}
fclose(fd);
}
}

u32 basm_rand()
{
int i, j, k;

i=basm_rand_pos;
j=(i+127-61)%127;
k=(i+127-31)%127;
basm_rand_state[i]^=basm_rand_state[j];
basm_rand_state[i]^=basm_rand_state[k];
basm_rand_pos=(i+1)%127;

return(basm_rand_state[i]);
}

char *basm_rand_key12()
{
static char buf[16];
u32 i;

i=basm_rand();
buf[0]=basm_base48[(i/254803968)%48];
buf[1]=basm_base48[(i/5308416)%48];
buf[2]=basm_base48[(i/110592)%48];
buf[3]=basm_base48[(i/2304)%48];
buf[4]=basm_base48[(i/48)%48];
buf[5]=basm_base48[ i%48];

i=basm_rand();
buf[ 6]=basm_base48[(i/254803968)%48];
buf[ 7]=basm_base48[(i/5308416)%48];
buf[ 8]=basm_base48[(i/110592)%48];
buf[ 9]=basm_base48[(i/2304)%48];
buf[10]=basm_base48[(i/48)%48];
buf[11]=basm_base48[ i%48];

buf[12]=0;

return(buf);
}

char *basm_rand_key18()
{
static char buf[24];
u32 i;

i=basm_rand();
buf[0]=basm_base48[(i/254803968)%48];
buf[1]=basm_base48[(i/5308416)%48];
buf[2]=basm_base48[(i/110592)%48];
buf[3]=basm_base48[(i/2304)%48];
buf[4]=basm_base48[(i/48)%48];
buf[5]=basm_base48[ i%48];

i=basm_rand();
buf[ 6]=basm_base48[(i/254803968)%48];
buf[ 7]=basm_base48[(i/5308416)%48];
buf[ 8]=basm_base48[(i/110592)%48];
buf[ 9]=basm_base48[(i/2304)%48];
buf[10]=basm_base48[(i/48)%48];
buf[11]=basm_base48[ i%48];

i=basm_rand();
buf[12]=basm_base48[(i/254803968)%48];
buf[13]=basm_base48[(i/5308416)%48];
buf[14]=basm_base48[(i/110592)%48];
buf[15]=basm_base48[(i/2304)%48];
buf[16]=basm_base48[(i/48)%48];
buf[17]=basm_base48[ i%48];

buf[18]=0;

return(buf);
}



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