disk/part.c: 'usb storage' avoiding overflow when output capacity

Before: Marvell>> usb storage Device 0: Vendor: StoreJet Rev: Prod: Transcend Type: Hard Disk Capacity: 28759.9 MB = 28.0 GB (488397168 x 512) After: Marvell>> usb storage Device 0: Vendor: StoreJet Rev: Prod: Transcend Type: Hard Disk Capacity: 238475.1 MB = 232.8 GB (488397168 x 512) Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

disk/part.c: 'usb storage' avoiding overflow when output capacity
Before: Marvell>> usb storage Device 0: Vendor: StoreJet Rev: Prod: Transcend Type: Hard Disk Capacity: 28759.9 MB = 28.0 GB (488397168 x 512) After: Marvell>> usb storage Device 0: Vendor: StoreJet Rev: Prod: Transcend Type: Hard Disk Capacity: 238475.1 MB = 232.8 GB (488397168 x 512) Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Sergei Trofimovich · Wolfgang Denk
1 parent b9d51fbb18
Showing 1 changed file with 23 additions and 5 deletions Side-by-side Diff
disk/part.c
@@ -109,14 +109,31 @@
 /*
  * reports device info to the user
  */
-void dev_print (block_dev_desc_t *dev_desc)
-{
+
 #ifdef CONFIG_LBA48
-	uint64_t lba512; /* number of blocks if 512bytes block size */
+typedef uint64_t lba512_t;
 #else
-	lbaint_t lba512;
+typedef lbaint_t lba512_t;
 #endif
  
+/*
+ * Overflowless variant of (block_count * mul_by / div_by)
+ * when div_by > mul_by
+ */
+static lba512_t lba512_muldiv (lba512_t block_count, lba512_t mul_by, lba512_t div_by)
+{
+	lba512_t bc_quot, bc_rem;
+
+	/* x * m / d == x / d * m + (x % d) * m / d */
+	bc_quot = block_count / div_by;
+	bc_rem  = block_count - div_by * bc_quot;
+	return bc_quot * mul_by + (bc_rem * mul_by) / div_by;
+}
+
+void dev_print (block_dev_desc_t *dev_desc)
+{
+	lba512_t lba512; /* number of blocks if 512bytes block size */
+
 	if (dev_desc->type == DEV_TYPE_UNKNOWN) {
 		puts ("not available\n");
 		return;
  
@@ -184,8 +201,9 @@
 		lba = dev_desc->lba;
  
 		lba512 = (lba * (dev_desc->blksz/512));
-		mb = (10 * lba512) / 2048;	/* 2048 = (1024 * 1024) / 512 MB */
 		/* round to 1 digit */
+		mb = lba512_muldiv(lba512, 10, 2048);	/* 2048 = (1024 * 1024) / 512 MB */
+
 		mb_quot	= mb / 10;
 		mb_rem	= mb - (10 * mb_quot);
...	...	@@ -109,14 +109,31 @@
109	109	/*
110	110	* reports device info to the user
111	111	*/
112		-void dev_print (block_dev_desc_t *dev_desc)
113		-{
	112	+
114	113	#ifdef CONFIG_LBA48
115		- uint64_t lba512; /* number of blocks if 512bytes block size */
	114	+typedef uint64_t lba512_t;
116	115	#else
117		- lbaint_t lba512;
	116	+typedef lbaint_t lba512_t;
118	117	#endif
119	118
	119	+/*
	120	+ * Overflowless variant of (block_count * mul_by / div_by)
	121	+ * when div_by > mul_by
	122	+ */
	123	+static lba512_t lba512_muldiv (lba512_t block_count, lba512_t mul_by, lba512_t div_by)
	124	+{
	125	+ lba512_t bc_quot, bc_rem;
	126	+
	127	+ /* x * m / d == x / d * m + (x % d) * m / d */
	128	+ bc_quot = block_count / div_by;
	129	+ bc_rem = block_count - div_by * bc_quot;
	130	+ return bc_quot * mul_by + (bc_rem * mul_by) / div_by;
	131	+}
	132	+
	133	+void dev_print (block_dev_desc_t *dev_desc)
	134	+{
	135	+ lba512_t lba512; /* number of blocks if 512bytes block size */
	136	+
120	137	if (dev_desc->type == DEV_TYPE_UNKNOWN) {
121	138	puts ("not available\n");
122	139	return;
123	140
...	...	@@ -184,8 +201,9 @@
184	201	lba = dev_desc->lba;
185	202
186	203	lba512 = (lba * (dev_desc->blksz/512));
187		- mb = (10 * lba512) / 2048; /* 2048 = (1024 * 1024) / 512 MB */
188	204	/* round to 1 digit */
	205	+ mb = lba512_muldiv(lba512, 10, 2048); /* 2048 = (1024 * 1024) / 512 MB */
	206	+
189	207	mb_quot = mb / 10;
190	208	mb_rem = mb - (10 * mb_quot);
191	209