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D297 M-150: eeprom-shim migration of pre-D284 save CRCs
v0.3.0 silently wiped all v0.2.x saves on first launch: stored slot CRCs are fingerprints of the PRNG that wrote them, and D284 changed the PRNG. One-time migration in the eeprom shim's read path (block 4 only): a slot that fails the current-CRC check but validates under the legacy PRNG is re-stamped with current-PRNG checksums before fileValidateSaves sees it, then persisted once. Runs before geEepromPatchAllCheats so cheat patches never reach the file. Corrupt/fresh slots untouched (game's own wipe path). - port/src/legacycrc.c: isolated file carrying the deliberately-wrong pre-D284 PRNG (verbatim from 0de99b4d^, reviewer-verified bit-exact) + lockstep copy of the crc.c loop; header says when it may be deleted. - tools_pc/d295_crc.py: reference CRC model, bit-exact vs compiled C for both PRNGs (used to verify migrated files). Verified: user's #87 artifact migrates 5/5 slots with progress intact and is idempotent on relaunch; native post-fix saves, corrupt slots, and fresh eeps all behave per design; 21/21 sweep PASS.
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@@ -0,0 +1,106 @@
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/*
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* port/src/legacycrc.c — D297: one-time migration of pre-D284 save-slot CRCs.
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*
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* WHY A DELIBERATELY-WRONG PRNG LIVES IN THIS TREE (read before "fixing" it):
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*
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* v0.2.x shipped with a port-side bug in randomGetNextFrom's dsll32/dsrl32
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* semantics (modelled as 32-bit shifts; real MIPS64 shifts by n+32 over the
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* full register). D284 (commit 0de99b4d) fixed it. But fileGenerateCRC
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* (src/game/crc.c) runs that PRNG off a LOCAL constant seed, so every slot
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* checksum stored on disk is a fingerprint of the PRNG implementation that
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* wrote it: saves written by v0.2.x validate under the OLD stream and fail
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* the NEW one, and fileValidateSaves wipes failing slots (D295/M-148, D297).
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*
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* This file carries the pre-D284 transform so the eeprom shim can recognize
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* a legacy save (old-CRC match) and re-stamp its two checksum words with the
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* current-PRNG values before the game validates. No game files are touched;
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* the new CRCs come from the game's own fileGenerateCRC — only the OLD PRNG
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* is duplicated here, and it must stay bit-exact-WRONG. Do not "fix" the
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* shifts below; do not share helpers with port/src/random.c.
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*
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* When this can be deleted: once no pre-D284 saves are expected in the wild
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* (the v0.3.0 release is the last build that meets them un-migrated). Keep
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* it at least until then; the cost is ~60 lines of dead-but-harmless code.
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*
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* Verification: the legacy stream below was re-derived from
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* `git show 0de99b4d^:port/src/random.c` and matches tools_pc/d295_crc.py,
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* which is bit-exact against compiled C for both PRNGs (see D295 M-148).
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*/
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#include <ultra64.h>
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#include "file.h" /* save_data */
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extern void fileGenerateCRC(u8 *addressA, u8 *addressB, save_data *retval);
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/* Pre-D284 randomGetNextFrom: verbatim body from 0de99b4d^:port/src/random.c
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* with the OLD helper semantics inlined ((x << n) & 0xFFFFFFFF etc.). */
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static u32 geLegacyRandomGetNextFrom(u64 *seed)
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{
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u64 a3 = *seed;
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u64 a1, a2;
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a2 = (a3 << 0x1f) & 0xFFFFFFFFULL; /* dsll32, pre-D284 semantics */
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a1 = a3 << 0x1f; /* dsll */
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a2 = a2 >> 0x1f; /* dsrl */
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a1 = (a1 >> 0) & 0xFFFFFFFFULL; /* dsrl32, pre-D284 semantics */
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a3 = (a3 << 0xc) & 0xFFFFFFFFULL; /* dsll32, pre-D284 semantics */
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a2 = a2 | a1;
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a3 = (a3 >> 0) & 0xFFFFFFFFULL; /* dsrl32, pre-D284 semantics */
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a2 = a2 ^ a3;
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a3 = a2 >> 0x14; /* dsrl */
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a3 = a3 & 0xfff;
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a3 = a3 ^ a2;
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*seed = a3;
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return (u32)a3;
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}
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/* Same loop as fileGenerateCRC (src/game/crc.c) stepping the legacy PRNG.
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* Keep in lockstep with crc.c if that loop ever changes. */
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static void geLegacyGenerateCRC(u8 *addressA, u8 *addressB, save_data *retval)
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{
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u8 *byte;
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s32 shift = 0;
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s64 polynormal = 0x8F809F473108B3C1; /* same local constant seed as crc.c */
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s32 checksum1 = 0;
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s32 checksum2 = 0;
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for (byte = addressA; byte < addressB; byte++, shift += 7) {
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polynormal += *byte << (shift & 0xF);
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checksum1 ^= geLegacyRandomGetNextFrom(&polynormal);
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}
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for (byte = addressB - 1; byte >= addressA; byte--, shift += 3) {
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polynormal += *byte << (shift & 0xF);
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checksum2 ^= geLegacyRandomGetNextFrom(&polynormal);
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}
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retval->chksum1 = checksum1;
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retval->chksum2 = checksum2;
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}
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/* Migrate up to five consecutive 96-byte save slots in place. A slot is
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* migrated iff it FAILS the current-PRNG check but PASSES the legacy one;
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* re-stamped via the game's own fileGenerateCRC. Corrupt slots (fail both)
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* are left alone for the game's own wipe path. Returns the count migrated. */
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int geLegacyCrcMaybeMigrateSlots(u8 *slots5)
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{
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save_data *slots = (save_data *)slots5;
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int migrated = 0;
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for (int i = 0; i < 5; i++) {
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save_data calc = {0}; /* only chksum1/chksum2 are read back */
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u8 *a = &slots[i].completion_bitflags; /* slot bytes [8..96) */
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u8 *b = (u8 *)&slots[i + 1]; /* end boundary, never dereferenced */
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fileGenerateCRC(a, b, &calc);
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if (calc.chksum1 == slots[i].chksum1 && calc.chksum2 == slots[i].chksum2)
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continue; /* current-PRNG save (or already migrated) — idempotent no-op */
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geLegacyGenerateCRC(a, b, &calc);
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if (calc.chksum1 != slots[i].chksum1 || calc.chksum2 != slots[i].chksum2)
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continue; /* corrupt: game's fileValidateSaves handles it */
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fileGenerateCRC(a, b, &slots[i]); /* re-stamp chksum1/chksum2 in place */
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migrated++;
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}
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return migrated;
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}
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@@ -1225,6 +1225,8 @@ typedef char ge_save_slot_size_check[(sizeof(ge_save_slot) == 96) ? 1 : -1];
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* re-checks after the block read. */
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extern void fileGenerateCRC(u8 *addressA, u8 *addressB, void *retval);
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extern int geLegacyCrcMaybeMigrateSlots(u8 *slots5); /* port/src/legacycrc.c (D297) */
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extern s32 portAllUnlocked; /* port/src/video.c */
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/* Bit math mirrors fileGetSaveStageDifficultyTime / fileSetDifficultyStageTime
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@@ -1337,6 +1339,23 @@ static s32 geEepromRW(u8 block, u8 *buf, int nbytes, int write)
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geEepromStore();
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} else {
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memcpy(buf, s_eeprom + off, nbytes);
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/* D297: one-time migration of pre-D284 slot CRCs (port/src/legacycrc.c).
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* This IS the read fileValidateSaves performs (block 4, five slots), so
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* the re-stamped checksums are exactly what the game validates — no
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* ordering hazard. Runs BEFORE geEepromPatchAllCheats so that only
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* pristine+migrated bytes are ever persisted; AllUnlocked patches stay
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* read-time-only as before. Block-0 smallSave is deliberately untouched
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* (factory seal, see D297). */
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if (block == 4 && nbytes == (int)(sizeof(ge_save_slot) * 5)) {
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int migrated = geLegacyCrcMaybeMigrateSlots(buf);
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if (migrated) {
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memcpy(s_eeprom + off, buf, nbytes);
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geEepromStore();
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sysLogPrintf(LOG_INFO,
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"eeprom: D297-migrated %d pre-D284 save slot(s) to current CRC",
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migrated);
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}
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}
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/* fileValidateSaves' block read: five save slots from block 4. */
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if (portAllUnlocked && block == 4 &&
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nbytes == (int)(sizeof(ge_save_slot) * 5)) {
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@@ -0,0 +1,84 @@
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#!/usr/bin/env python3
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"""D295/M-148: reproduce fileGenerateCRC (src/game/crc.c) with both the pre-D284
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(buggy, shipped in v0.2.x) and post-D284 (HEAD) PRNG semantics, verify against the
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user's saved slot CRCs, and emit a patched eep whose slots carry POST-FIX CRCs so
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a HEAD build accepts them (proves the difficultytext overflow is still live).
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Save layout in ge007.eep (verified M-148):
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bytes 0..31 : smallSave header (block 0)
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slot i : file offset 32 + i*96, i = 0..5 (sizeof(save_data)=96, padded)
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slot fields : c1(s32) c2(s32) bitflags(1) flag_007(1) music(1) sfx(1)
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options(2) cheats(3) pad(1) times[76]
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CRC region : &completion_bitflags .. save+1 => slot bytes [8..96), 88 bytes.
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"""
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import struct, sys
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M64 = (1 << 64) - 1
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def make_rng(buggy: bool):
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def dsll32(x, n):
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if buggy: return (x << n) & 0xFFFFFFFF
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return (x << (n + 32)) & M64
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def dsrl32(x, n):
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if buggy: return (x >> n) & 0xFFFFFFFF
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return x >> (n + 32)
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def step(seed: int) -> int:
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# Mirrors randomGetNextFrom line-by-line. NOTE the plain dsrl/dsll lines
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# (a2 >>= 31, a1 = a3 << 31, a2 >>= 20) are NOT the *32 helpers.
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a3 = seed & M64
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a2 = dsll32(a3, 0x1F) >> 0x1F # dsll32 then plain dsrl 31
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a1 = dsrl32((a3 << 0x1F) & M64, 0) # plain dsll 31 then dsrl32 0
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a3 = dsrl32(dsll32(a3, 0xC), 0) # dsll32 then dsrl32 0
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a2 = (a2 | a1) ^ a3
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a3 = ((a2 >> 0x14) & 0xFFF) ^ a2 # plain dsrl 20, andi, xor
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return a3 & M64
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return step
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def file_generate_crc(data: bytes, buggy: bool):
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"""Mirror crc.c exactly: shift is NOT reset between the two passes."""
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step = make_rng(buggy)
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poly = 0x8F809F473108B3C1 & M64
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c1 = 0; c2 = 0; shift = 0
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for b in data: # forward pass, +7/byte
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poly = (poly + ((b << (shift & 0xF)) & M64)) & M64
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shift += 7
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poly = step(poly) # randomGetNextFrom updates the seed IN PLACE
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c1 ^= poly & 0xFFFFFFFF
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for b in reversed(data): # backward pass, +3/byte, shift continues
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poly = (poly + ((b << (shift & 0xF)) & M64)) & M64
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shift += 3
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poly = step(poly)
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c2 ^= poly & 0xFFFFFFFF
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return c1 & 0xFFFFFFFF, c2 & 0xFFFFFFFF
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def main():
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src = sys.argv[1] if len(sys.argv) > 1 else r"C:\Users\james\Downloads\ge-issue87-artifacts\ge007.eep"
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dst = sys.argv[2] if len(sys.argv) > 2 else None
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eep = bytearray(open(src, "rb").read())
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assert len(eep) == 2048, len(eep)
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print("slot | stored c1,c2 | oldPRNG c1,c2 | newPRNG c1,c2 | old? new?")
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ok_old = ok_new = True
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for i in range(5):
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off = 32 + i * 96
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sc1, sc2 = struct.unpack_from("<II", eep, off)
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region = bytes(eep[off + 8: off + 96])
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oc1, oc2 = file_generate_crc(region, buggy=True)
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nc1, nc2 = file_generate_crc(region, buggy=False)
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o = (oc1, oc2) == (sc1, sc2); n = (nc1, nc2) == (sc1, sc2)
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ok_old &= o; ok_new &= n
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print(f" {i} | {sc1:08x},{sc2:08x} | {oc1:08x},{oc2:08x} | {nc1:08x},{nc2:08x} | {o=} {n=}")
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print(f"old PRNG matches all 5 stored CRCs: {ok_old}")
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print(f"new PRNG matches all 5 stored CRCs: {ok_new}")
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if dst:
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for i in range(5):
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off = 32 + i * 96
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region = bytes(eep[off + 8: off + 96])
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nc1, nc2 = file_generate_crc(region, buggy=False)
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struct.pack_into("<II", eep, off, nc1, nc2)
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open(dst, "wb").write(eep)
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print(f"patched (post-fix CRCs, slots 0-4) -> {dst}")
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if __name__ == "__main__":
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main()
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