From b0a2df6190a37fcc112f6599ccf021c49d11ed6c Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sat, 29 Jul 2017 22:48:37 -0700
Subject: [PATCH] GB MBC: Fix RTC loading when file size is off

---
 CHANGES      |  1 +
 src/gb/mbc.c | 13 +++----------
 2 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/CHANGES b/CHANGES
index ca130fb38..a1a15ec86 100644
--- a/CHANGES
+++ b/CHANGES
@@ -12,6 +12,7 @@ Bugfixes:
  - GB Memory: Prevent accessing empty SRAM (fixes mgba.io/i/831)
  - GB, GBA: Fix crashes when attempting to identify null VFiles
  - GB MBC: Fix RTC initialization (fixes mgba.io/i/825)
+ - GB MBC: Fix RTC loading when file size is off
 Misc:
  - Qt: Don't rebuild library view if style hasn't changed
  - SDL: Fix 2.0.5 build on macOS under some circumstances
diff --git a/src/gb/mbc.c b/src/gb/mbc.c
index 4b7e93626..0c51b1a5f 100644
--- a/src/gb/mbc.c
+++ b/src/gb/mbc.c
@@ -768,17 +768,10 @@ void GBMBCRTCRead(struct GB* gb) {
 	if (!vf) {
 		return;
 	}
-	ssize_t end = vf->seek(vf, -sizeof(rtcBuffer), SEEK_END);
-	switch (end & 0x1FFF) {
-	case 0:
-		break;
-	case 0x1FFC:
-		vf->seek(vf, -sizeof(rtcBuffer) - 4, SEEK_END);
-		break;
-	default:
+	vf->seek(vf, gb->sramSize, SEEK_SET);
+	if (vf->read(vf, &rtcBuffer, sizeof(rtcBuffer)) < (ssize_t) sizeof(rtcBuffer) - 4) {
 		return;
 	}
-	vf->read(vf, &rtcBuffer, sizeof(rtcBuffer));
 
 	LOAD_32LE(gb->memory.rtcRegs[0], 0, &rtcBuffer.latchedSec);
 	LOAD_32LE(gb->memory.rtcRegs[1], 0, &rtcBuffer.latchedMin);
@@ -812,7 +805,7 @@ void GBMBCRTCWrite(struct GB* gb) {
 	STORE_32LE(gb->memory.rtcRegs[4], 0, &rtcBuffer.latchedDaysHi);
 	STORE_64LE(gb->memory.rtcLastLatch, 0, &rtcBuffer.unixTime);
 
-	if (vf->size(vf) == gb->sramSize) {
+	if ((size_t) vf->size(vf) < gb->sramSize + sizeof(rtcBuffer)) {
 		// Writing past the end of the file can invalidate the file mapping
 		vf->unmap(vf, gb->memory.sram, gb->sramSize);
 		gb->memory.sram = NULL;