SDL/src/SDL_utils.c

/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/
#include "SDL_internal.h"

#include "SDL_utils_c.h"

/* Common utility functions that aren't in the public API */

int SDL_powerof2(int x)
{
    int value;

    if (x <= 0) {
        /* Return some sane value - we shouldn't hit this in our use cases */
        return 1;
    }

    /* This trick works for 32-bit values */
    {
        SDL_COMPILE_TIME_ASSERT(SDL_powerof2, sizeof(x) == sizeof(Uint32));
    }
    value = x;
    value -= 1;
    value |= value >> 1;
    value |= value >> 2;
    value |= value >> 4;
    value |= value >> 8;
    value |= value >> 16;
    value += 1;

    return value;
}

// Algorithm adapted with thanks from John Cook's blog post:
// http://www.johndcook.com/blog/2010/10/20/best-rational-approximation
void SDL_CalculateFraction(float x, int *numerator, int *denominator)
{
    const int N = 1000;
    int a = 0, b = 1;
    int c = 1, d = 0;

    while (b <= N && d <= N) {
        float mediant = (float)(a + c) / (b + d);
        if (x == mediant) {
            if (b + d <= N) {
                *numerator = a + c;
                *denominator = b + d;
            } else if (d > b) {
                *numerator = c;
                *denominator = d;
            } else {
                *numerator = a;
                *denominator = b;
            }
            return;
        } else if (x > mediant) {
            a = a + c;
            b = b + d;
        } else {
            c = a + c;
            d = b + d;
        }
    }
    if (b > N) {
        *numerator = c;
        *denominator = d;
    } else {
        *numerator = a;
        *denominator = b;
    }
}

SDL_bool SDL_endswith(const char *string, const char *suffix)
{
    size_t string_length = string ? SDL_strlen(string) : 0;
    size_t suffix_length = suffix ? SDL_strlen(suffix) : 0;

    if (suffix_length > 0 && suffix_length <= string_length) {
        if (SDL_memcmp(string + string_length - suffix_length, suffix, suffix_length) == 0) {
            return SDL_TRUE;
        }
    }
    return SDL_FALSE;
}