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Fixed bug 4283 - SDL's version of memset is different from libc's 

janisozaur

memset's documentation reads:

* The memset() function shall copy c (converted to an unsigned char) into each of the first n bytes of the object pointed to by s. (http://pubs.opengroup.org/onlinepubs/9699919799/functions/memset.html)
* Sets the first count characters of dest to the character c. (https://msdn.microsoft.com/en-us/library/1fdeehz6.aspx)
* write a byte to a byte string (https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/memset.3.html)

The highlight here is they all mean a single _byte_, even though memset receives a parameter of type int, which can hold more data than a single byte. SDL's implementation of memset, however, does not clear any of the higher bits, causing an erroneous behaviour when passed an argument bigger than 0xff.
This commit is contained in:
Sam Lantinga 2018-09-28 20:48:18 -07:00
parent 74638ea3c5
commit 9e8e0fb7b1
1 changed files with 7 additions and 2 deletions
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9
src/stdlib/SDL_string.c
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@ -271,12 +271,16 @@ SDL_memset(SDL_OUT_BYTECAP(len) void *dst, int c, size_t len)
size_t left;
Uint32 *dstp4;
Uint8 *dstp1 = (Uint8 *) dst;
Uint32 value4 = (c | (c << 8) | (c << 16) | (c << 24));
Uint8 value1 = (Uint8) c;
Uint8 value1;
Uint32 value4;
/* The value used in memset() is a byte, passed as an int */
c &= 0xff;
/* The destination pointer needs to be aligned on a 4-byte boundary to
* execute a 32-bit set. Set first bytes manually if needed until it is
* aligned. */
value1 = (Uint8)c;
while ((intptr_t)dstp1 & 0x3) {
if (len--) {
*dstp1++ = value1;
@ -285,6 +289,7 @@ SDL_memset(SDL_OUT_BYTECAP(len) void *dst, int c, size_t len)
}
}
value4 = (c | (c << 8) | (c << 16) | (c << 24));
dstp4 = (Uint32 *) dstp1;
left = (len % 4);
len /= 4;