iphone - float ，负零？

Question

我正在为我的游戏设置音效音量。我希望音量以 0.1 为增量从 0.0 变为 1.0。

但是，当它达到零时，我的日志反而告诉我它是 -0.00000 并继续倒计时。请告诉我哪里出了问题。谢谢

-(void)sfxUp{
     NSLog(@"SFX UP %f",[[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]);
    if ([[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"] == 1.0f)
        return;
    [[NSUserDefaults standardUserDefaults]setFloat:([[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]+0.1f) forKey:@"sfx_volume"];
    [[NSUserDefaults standardUserDefaults]synchronize];
    [[SimpleAudioEngine sharedEngine] setEffectsVolume:[[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]];
    NSLog(@"SFX UP %f",[[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]);
}
-(void)sfxDown{
    NSLog(@"SFX DOWN %f",[[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]);
    if ([[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"] == 0.0f)
        return;
    [[NSUserDefaults standardUserDefaults]setFloat:([[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]-0.1f) forKey:@"sfx_volume"];
    [[NSUserDefaults standardUserDefaults]synchronize];
    [[SimpleAudioEngine sharedEngine] setEffectsVolume:[[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]];
     NSLog(@"SFX DOWN %f",[[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]);
}

仅单击“降低音量”按钮，这是我的日志输出:

2012-06-13 18:32:25.067 Bomb Defuse[80558:1c403] SFX DOWN 1.000000
2012-06-13 18:32:25.068 Bomb Defuse[80558:1c403] SFX DOWN 0.900000
2012-06-13 18:32:25.385 Bomb Defuse[80558:1c403] SFX DOWN 0.900000
2012-06-13 18:32:25.386 Bomb Defuse[80558:1c403] SFX DOWN 0.800000
2012-06-13 18:32:25.623 Bomb Defuse[80558:1c403] SFX DOWN 0.800000
2012-06-13 18:32:25.624 Bomb Defuse[80558:1c403] SFX DOWN 0.700000
2012-06-13 18:32:25.873 Bomb Defuse[80558:1c403] SFX DOWN 0.700000
2012-06-13 18:32:25.874 Bomb Defuse[80558:1c403] SFX DOWN 0.600000
2012-06-13 18:32:26.116 Bomb Defuse[80558:1c403] SFX DOWN 0.600000
2012-06-13 18:32:26.140 Bomb Defuse[80558:1c403] SFX DOWN 0.500000
2012-06-13 18:32:26.346 Bomb Defuse[80558:1c403] SFX DOWN 0.500000
2012-06-13 18:32:26.348 Bomb Defuse[80558:1c403] SFX DOWN 0.400000
2012-06-13 18:32:26.605 Bomb Defuse[80558:1c403] SFX DOWN 0.400000
2012-06-13 18:32:26.608 Bomb Defuse[80558:1c403] SFX DOWN 0.300000
2012-06-13 18:32:26.835 Bomb Defuse[80558:1c403] SFX DOWN 0.300000
2012-06-13 18:32:26.838 Bomb Defuse[80558:1c403] SFX DOWN 0.200000
2012-06-13 18:32:27.068 Bomb Defuse[80558:1c403] SFX DOWN 0.200000
2012-06-13 18:32:27.069 Bomb Defuse[80558:1c403] SFX DOWN 0.100000
2012-06-13 18:32:27.319 Bomb Defuse[80558:1c403] SFX DOWN 0.100000
2012-06-13 18:32:27.338 Bomb Defuse[80558:1c403] SFX DOWN -0.000000
2012-06-13 18:32:27.630 Bomb Defuse[80558:1c403] SFX DOWN -0.000000
2012-06-13 18:32:27.640 Bomb Defuse[80558:1c403] SFX DOWN -0.100000
2012-06-13 18:32:27.946 Bomb Defuse[80558:1c403] SFX DOWN -0.100000
2012-06-13 18:32:27.947 Bomb Defuse[80558:1c403] SFX DOWN -0.200000
2012-06-13 18:32:28.170 Bomb Defuse[80558:1c403] SFX DOWN -0.200000
2012-06-13 18:32:28.172 Bomb Defuse[80558:1c403] SFX DOWN -0.300000
2012-06-13 18:32:28.414 Bomb Defuse[80558:1c403] SFX DOWN -0.300000
2012-06-13 18:32:28.416 Bomb Defuse[80558:1c403] SFX DOWN -0.400000
2012-06-13 18:32:28.641 Bomb Defuse[80558:1c403] SFX DOWN -0.400000
2012-06-13 18:32:28.643 Bomb Defuse[80558:1c403] SFX DOWN -0.500000
2012-06-13 18:32:28.869 Bomb Defuse[80558:1c403] SFX DOWN -0.500000
2012-06-13 18:32:28.870 Bomb Defuse[80558:1c403] SFX DOWN -0.600000
2012-06-13 18:32:29.301 Bomb Defuse[80558:1c403] SFX DOWN -0.600000
2012-06-13 18:32:29.303 Bomb Defuse[80558:1c403] SFX DOWN -0.700000
2012-06-13 18:32:29.584 Bomb Defuse[80558:1c403] SFX DOWN -0.700000
2012-06-13 18:32:29.586 Bomb Defuse[80558:1c403] SFX DOWN -0.800000

编辑:

更改为 >= 和 <=(分别)有以下输出:

2012-06-13 18:45:34.574 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:35.135 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:35.529 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:35.877 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:36.057 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:36.229 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:36.391 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:36.542 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:36.717 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:36.897 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:37.599 Bomb Defuse[80607:1c403] BG DOWN1.000000
2012-06-13 18:45:37.602 Bomb Defuse[80607:1c403] BG DOWN0.900000
2012-06-13 18:45:38.431 Bomb Defuse[80607:1c403] BG DOWN0.900000
2012-06-13 18:45:38.491 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:38.617 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:38.951 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:39.125 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:39.479 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:39.908 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:40.399 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:40.624 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:40.841 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:41.059 Bomb Defuse[80607:1c403] BG DOWN-0.100000

Answer 1

浮点运算并不精确——从 1.0 开始减去 0.1 十次不一定会得到精确的 0.0。更多细节，阅读经典论文What Every Computer Scientist Should Know About Floating-Point Arithmetic .

您可以通过将值限制为 [0.0, 1.0] 来解决此问题当它改变时，通过避免严格相等比较(例如，使用 >= 或 <= 而不是 == )，或者 - 理想情况下 - 通过简单地将体积存储为 0 到 10 之间的整数，并除以需要时为 10.0。