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move contents of do while loop in nbt_nexttag into its own funciton

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Quinn
2025-08-22 09:58:45 +02:00
parent 949cac5bfe
commit 9996e84ef5
1 changed files with 44 additions and 34 deletions
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78
src/dat/nbt.c
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@@ -37,6 +37,48 @@ static const u8 *nexttag_list(const u8 *restrict ptr, uint *restrict const dpt,
return ptr; return ptr;
} }
/* increments to the next tag and returns it (or `NULL`)
* - `tag` represents the start of the tag, e.i. The tag ID, or in the case of `NBT_LIST` data, the start of this data.
* - `dpt` shall point to the "depth" we're at, this is used as index for `lens` and `tags`
* - `lens` shall contain `MAX_DEPTH` of items representing the list length, if the current item is non-zero we shall assume we're in a list.
* Where the value is decremented until we reach `0`.
* - `tags` shall contain `MAX_DEPTH` of items representing the list's stored type. */
static const u8 *nexttag(const u8 *restrict tag, uint *restrict const dpt, i32 *restrict const lens, u8 *restrict const tags) {
u8 type;
const u8 *ptr = tag;
if (lens[*dpt]) {
type = tags[*dpt];
lens[*dpt]--;
*dpt -= !lens[*dpt];
} else {
type = *tag;
ptr += be16toh(*(u16 *)(tag + 1)) + 3;
}
switch (type) {
case NBT_I8: ptr += 1; break;
case NBT_I16: ptr += 2; break;
case NBT_I32: // fall through
case NBT_F32: ptr += 4; break;
case NBT_I64: // fall through
case NBT_F64: ptr += 8; break;
case NBT_ARR_I8: ptr += 4 + (i32)be32toh(*(u32 *)ptr) * 1; break;
case NBT_ARR_I32: ptr += 4 + (i32)be32toh(*(u32 *)ptr) * 4; break;
case NBT_ARR_I64: ptr += 4 + (i32)be32toh(*(u32 *)ptr) * 8; break;
case NBT_STR: ptr += 2 + (u16)be16toh(*(u16 *)ptr) * 1; break;
case NBT_END: (*dpt)--; break;
case NBT_COMPOUND: (*dpt)++; break;
case NBT_LIST: ptr = nexttag_list(ptr, dpt, lens, tags); break;
default: return NULL; // unexpected value; buffer is likely corrupt
}
return ptr;
}
/* TODO: write test cases for this function: /* TODO: write test cases for this function:
* - list:compound... * - list:compound...
* - non-existent type * - non-existent type
@@ -44,46 +86,14 @@ static const u8 *nexttag_list(const u8 *restrict ptr, uint *restrict const dpt,
* - string * - string
*/ */
const u8 *nbt_nexttag(const u8 *restrict buf) { const u8 *nbt_nexttag(const u8 *restrict buf) {
const u8 *tag, *ptr; const u8 *tag;
u8 tags[MAX_DEPTH] = {0}; u8 tags[MAX_DEPTH] = {0};
i32 lens[MAX_DEPTH] = {0}; i32 lens[MAX_DEPTH] = {0};
uint dpt = 0; uint dpt = 0;
u8 type;
tag = buf; tag = buf;
do { do {
ptr = tag; tag = nexttag(tag, &dpt, lens, tags);
if (lens[dpt]) {
type = tags[dpt];
lens[dpt]--;
dpt -= !lens[dpt];
} else {
type = *tag;
ptr += be16toh(*(u16 *)(tag + 1)) + 3;
}
switch (type) {
case NBT_I8: ptr += 1; break;
case NBT_I16: ptr += 2; break;
case NBT_I32: // fall through
case NBT_F32: ptr += 4; break;
case NBT_I64: // fall through
case NBT_F64: ptr += 8; break;
case NBT_ARR_I8: ptr += 4 + (i32)be32toh(*(u32 *)ptr) * 1; break;
case NBT_ARR_I32: ptr += 4 + (i32)be32toh(*(u32 *)ptr) * 4; break;
case NBT_ARR_I64: ptr += 4 + (i32)be32toh(*(u32 *)ptr) * 8; break;
case NBT_STR: ptr += 2 + (u16)be16toh(*(u16 *)ptr) * 1; break;
case NBT_END: dpt--; break;
case NBT_COMPOUND: dpt++; break;
case NBT_LIST: ptr = nexttag_list(ptr, &dpt, lens, tags); break;
default: return NULL; // unexpected value; buffer is likely corrupt
}
tag = ptr;
} while (dpt > 0); } while (dpt > 0);
return tag; return tag;
} }