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// Copyright (c) 2024, Marvin Borner <dev@marvinborner.de>
// SPDX-License-Identifier: MIT
#include <log.h>
#include <impl.h>
#include <stdint.h>
// haskell by John Tromp
static void levenshtein_encode(size_t n, FILE *fp)
{
if (n == 0) {
fprintf(fp, "10");
return;
}
fprintf(fp, "1");
size_t length = (8 * sizeof(n)) - __builtin_clzll(n);
levenshtein_encode(length - 1, fp);
if (length == 1)
return;
for (size_t i = 1 << (length - 2); i != 0; i >>= 1)
fprintf(fp, "%d", (i & n) != 0);
}
static void encode(Term *term, FILE *fp)
{
switch (term->type) {
case ABS:
fprintf(fp, "00");
encode(term->u.abs.body, fp);
break;
case APP:
fprintf(fp, "01");
encode(term->u.app.lhs, fp);
encode(term->u.app.rhs, fp);
break;
case IDX:
levenshtein_encode(term->u.index, fp);
break;
default:
fatal("invalid type %d\n", term->type);
}
}
// by John Tromp
static size_t levenshtein_decode(FILE *fp)
{
if (getc(fp) == '0')
return 0;
size_t x, l = levenshtein_decode(fp);
for (x = 1; l--;)
x = 2 * x + (getc(fp) != '0');
return x;
}
static Term *decode(FILE *fp)
{
Term *res = 0;
char a = getc(fp);
if (a == '0') {
char b = getc(fp);
if (b == '0') {
res = term_new(ABS);
res->u.abs.body = decode(fp);
} else if (b == '1') {
res = term_new(APP);
res->u.app.lhs = decode(fp);
res->u.app.rhs = decode(fp);
}
} else if (a == '1') {
res = term_new(IDX);
res->u.index = levenshtein_decode(fp);
}
if (!res)
fatal("invalid parsing state!\n");
return res;
}
Impl impl_blc2(void)
{
return (Impl){
.name = "blc2",
.encode = encode,
.decode = decode,
};
}
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