Atlas - SDL_memset.c
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1/*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2025 Sam Lantinga <[email protected]>
4
5  This software is provided 'as-is', without any express or implied
6  warranty.  In no event will the authors be held liable for any damages
7  arising from the use of this software.
8
9  Permission is granted to anyone to use this software for any purpose,
10  including commercial applications, and to alter it and redistribute it
11  freely, subject to the following restrictions:
12
13  1. The origin of this software must not be misrepresented; you must not
14     claim that you wrote the original software. If you use this software
15     in a product, an acknowledgment in the product documentation would be
16     appreciated but is not required.
17  2. Altered source versions must be plainly marked as such, and must not be
18     misrepresented as being the original software.
19  3. This notice may not be removed or altered from any source distribution.
20*/
21#include "SDL_internal.h"
22
23
24#ifdef SDL_memset
25#undef SDL_memset
26#endif
27#if SDL_DYNAMIC_API
28#define SDL_memset SDL_memset_REAL
29#endif
30void *SDL_memset(SDL_OUT_BYTECAP(len) void *dst, int c, size_t len)
31{
32#if defined(__GNUC__) && (defined(HAVE_LIBC) && HAVE_LIBC)
33    return __builtin_memset(dst, c, len);
34#elif defined(HAVE_MEMSET)
35    return memset(dst, c, len);
36#else
37    size_t left;
38    Uint32 *dstp4;
39    Uint8 *dstp1 = (Uint8 *)dst;
40    Uint8 value1;
41    Uint32 value4;
42
43    // The value used in memset() is a byte, passed as an int
44    c &= 0xff;
45
46    /* The destination pointer needs to be aligned on a 4-byte boundary to
47     * execute a 32-bit set. Set first bytes manually if needed until it is
48     * aligned. */
49    value1 = (Uint8)c;
50    while ((uintptr_t)dstp1 & 0x3) {
51        if (len--) {
52            *dstp1++ = value1;
53        } else {
54            return dst;
55        }
56    }
57
58    value4 = ((Uint32)c | ((Uint32)c << 8) | ((Uint32)c << 16) | ((Uint32)c << 24));
59    dstp4 = (Uint32 *)dstp1;
60    left = (len % 4);
61    len /= 4;
62    while (len--) {
63        *dstp4++ = value4;
64    }
65
66    dstp1 = (Uint8 *)dstp4;
67    switch (left) {
68    case 3:
69        *dstp1++ = value1;
70        SDL_FALLTHROUGH;
71    case 2:
72        *dstp1++ = value1;
73        SDL_FALLTHROUGH;
74    case 1:
75        *dstp1++ = value1;
76    }
77
78    return dst;
79#endif // HAVE_MEMSET
80}
81
82// Note that memset() is a byte assignment and this is a 32-bit assignment, so they're not directly equivalent.
83void *SDL_memset4(void *dst, Uint32 val, size_t dwords)
84{
85#if defined(__APPLE__) && defined(HAVE_STRING_H)
86    memset_pattern4(dst, &val, dwords * 4);
87#elif defined(__GNUC__) && defined(__i386__)
88    int u0, u1, u2;
89    __asm__ __volatile__(
90        "cld \n\t"
91        "rep ; stosl \n\t"
92        : "=&D"(u0), "=&a"(u1), "=&c"(u2)
93        : "0"(dst), "1"(val), "2"(SDL_static_cast(Uint32, dwords))
94        : "memory");
95#else
96    size_t _n = (dwords + 3) / 4;
97    Uint32 *_p = SDL_static_cast(Uint32 *, dst);
98    Uint32 _val = (val);
99    if (dwords == 0) {
100        return dst;
101    }
102    switch (dwords % 4) {
103    case 0:
104        do {
105            *_p++ = _val;
106            SDL_FALLTHROUGH;
107        case 3:
108            *_p++ = _val;
109            SDL_FALLTHROUGH;
110        case 2:
111            *_p++ = _val;
112            SDL_FALLTHROUGH;
113        case 1:
114            *_p++ = _val;
115        } while (--_n);
116    }
117#endif
118    return dst;
119}
120
121/* The optimizer on Visual Studio 2005 and later generates memcpy() and memset() calls.
122   We will provide our own implementation if we're not building with a C runtime. */
123#ifndef HAVE_LIBC
124// NOLINTNEXTLINE(readability-redundant-declaration)
125extern void *memset(void *dst, int c, size_t len);
126#if defined(_MSC_VER) && !defined(__INTEL_LLVM_COMPILER)
127#pragma intrinsic(memset)
128#endif
129
130#if defined(_MSC_VER) && !defined(__clang__)
131#pragma function(memset)
132#endif
133// NOLINTNEXTLINE(readability-inconsistent-declaration-parameter-name)
134void *memset(void *dst, int c, size_t len)
135{
136    return SDL_memset(dst, c, len);
137}
138#endif // !HAVE_LIBC
139
140
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