Er meint wahrscheinlich, dass bestimmte reelle Zahlen nicht exakt als Gleitkommazahlen dargestellt werden können. Das ist aber völlig irrelevant für seine Anwendung.

Hier nochmal der Beweis:

Code: 
#include <cstdio>

int main(int argc, char* argv[])
{
    FILE* f = fopen("output.txt", "w");
    for (int n1 = 0; n1 < 256; ++n1) {
        float n2 = (float)n1 / 255;
        int   n3 =  (int)(n2 * 255);
        fprintf(f, "%3d -> %.6f -> %3d: %s\n", n1, n2, n3, (n3 == n1 ? "OK!" : "ERROR!"));
    }
    fclose(f);
    return 0;
}
Ausgabe:

Code: 
  0 -> 0.000000 ->   0: OK!
  1 -> 0.003922 ->   1: OK!
  2 -> 0.007843 ->   2: OK!
  3 -> 0.011765 ->   3: OK!
  4 -> 0.015686 ->   4: OK!
  5 -> 0.019608 ->   5: OK!
  6 -> 0.023529 ->   6: OK!
  7 -> 0.027451 ->   7: OK!
  8 -> 0.031373 ->   8: OK!
  9 -> 0.035294 ->   9: OK!
 10 -> 0.039216 ->  10: OK!
 11 -> 0.043137 ->  11: OK!
 12 -> 0.047059 ->  12: OK!
 13 -> 0.050980 ->  13: OK!
 14 -> 0.054902 ->  14: OK!
 15 -> 0.058824 ->  15: OK!
 16 -> 0.062745 ->  16: OK!
 17 -> 0.066667 ->  17: OK!
 18 -> 0.070588 ->  18: OK!
 19 -> 0.074510 ->  19: OK!
 20 -> 0.078431 ->  20: OK!
 21 -> 0.082353 ->  21: OK!
 22 -> 0.086275 ->  22: OK!
 23 -> 0.090196 ->  23: OK!
 24 -> 0.094118 ->  24: OK!
 25 -> 0.098039 ->  25: OK!
 26 -> 0.101961 ->  26: OK!
 27 -> 0.105882 ->  27: OK!
 28 -> 0.109804 ->  28: OK!
 29 -> 0.113725 ->  29: OK!
 30 -> 0.117647 ->  30: OK!
 31 -> 0.121569 ->  31: OK!
 32 -> 0.125490 ->  32: OK!
 33 -> 0.129412 ->  33: OK!
 34 -> 0.133333 ->  34: OK!
 35 -> 0.137255 ->  35: OK!
 36 -> 0.141176 ->  36: OK!
 37 -> 0.145098 ->  37: OK!
 38 -> 0.149020 ->  38: OK!
 39 -> 0.152941 ->  39: OK!
 40 -> 0.156863 ->  40: OK!
 41 -> 0.160784 ->  41: OK!
 42 -> 0.164706 ->  42: OK!
 43 -> 0.168627 ->  43: OK!
 44 -> 0.172549 ->  44: OK!
 45 -> 0.176471 ->  45: OK!
 46 -> 0.180392 ->  46: OK!
 47 -> 0.184314 ->  47: OK!
 48 -> 0.188235 ->  48: OK!
 49 -> 0.192157 ->  49: OK!
 50 -> 0.196078 ->  50: OK!
 51 -> 0.200000 ->  51: OK!
 52 -> 0.203922 ->  52: OK!
 53 -> 0.207843 ->  53: OK!
 54 -> 0.211765 ->  54: OK!
 55 -> 0.215686 ->  55: OK!
 56 -> 0.219608 ->  56: OK!
 57 -> 0.223529 ->  57: OK!
 58 -> 0.227451 ->  58: OK!
 59 -> 0.231373 ->  59: OK!
 60 -> 0.235294 ->  60: OK!
 61 -> 0.239216 ->  61: OK!
 62 -> 0.243137 ->  62: OK!
 63 -> 0.247059 ->  63: OK!
 64 -> 0.250980 ->  64: OK!
 65 -> 0.254902 ->  65: OK!
 66 -> 0.258824 ->  66: OK!
 67 -> 0.262745 ->  67: OK!
 68 -> 0.266667 ->  68: OK!
 69 -> 0.270588 ->  69: OK!
 70 -> 0.274510 ->  70: OK!
 71 -> 0.278431 ->  71: OK!
 72 -> 0.282353 ->  72: OK!
 73 -> 0.286275 ->  73: OK!
 74 -> 0.290196 ->  74: OK!
 75 -> 0.294118 ->  75: OK!
 76 -> 0.298039 ->  76: OK!
 77 -> 0.301961 ->  77: OK!
 78 -> 0.305882 ->  78: OK!
 79 -> 0.309804 ->  79: OK!
 80 -> 0.313726 ->  80: OK!
 81 -> 0.317647 ->  81: OK!
 82 -> 0.321569 ->  82: OK!
 83 -> 0.325490 ->  83: OK!
 84 -> 0.329412 ->  84: OK!
 85 -> 0.333333 ->  85: OK!
 86 -> 0.337255 ->  86: OK!
 87 -> 0.341176 ->  87: OK!
 88 -> 0.345098 ->  88: OK!
 89 -> 0.349020 ->  89: OK!
 90 -> 0.352941 ->  90: OK!
 91 -> 0.356863 ->  91: OK!
 92 -> 0.360784 ->  92: OK!
 93 -> 0.364706 ->  93: OK!
 94 -> 0.368627 ->  94: OK!
 95 -> 0.372549 ->  95: OK!
 96 -> 0.376471 ->  96: OK!
 97 -> 0.380392 ->  97: OK!
 98 -> 0.384314 ->  98: OK!
 99 -> 0.388235 ->  99: OK!
100 -> 0.392157 -> 100: OK!
101 -> 0.396078 -> 101: OK!
102 -> 0.400000 -> 102: OK!
103 -> 0.403922 -> 103: OK!
104 -> 0.407843 -> 104: OK!
105 -> 0.411765 -> 105: OK!
106 -> 0.415686 -> 106: OK!
107 -> 0.419608 -> 107: OK!
108 -> 0.423529 -> 108: OK!
109 -> 0.427451 -> 109: OK!
110 -> 0.431373 -> 110: OK!
111 -> 0.435294 -> 111: OK!
112 -> 0.439216 -> 112: OK!
113 -> 0.443137 -> 113: OK!
114 -> 0.447059 -> 114: OK!
115 -> 0.450980 -> 115: OK!
116 -> 0.454902 -> 116: OK!
117 -> 0.458824 -> 117: OK!
118 -> 0.462745 -> 118: OK!
119 -> 0.466667 -> 119: OK!
120 -> 0.470588 -> 120: OK!
121 -> 0.474510 -> 121: OK!
122 -> 0.478431 -> 122: OK!
123 -> 0.482353 -> 123: OK!
124 -> 0.486275 -> 124: OK!
125 -> 0.490196 -> 125: OK!
126 -> 0.494118 -> 126: OK!
127 -> 0.498039 -> 127: OK!
128 -> 0.501961 -> 128: OK!
129 -> 0.505882 -> 129: OK!
130 -> 0.509804 -> 130: OK!
131 -> 0.513726 -> 131: OK!
132 -> 0.517647 -> 132: OK!
133 -> 0.521569 -> 133: OK!
134 -> 0.525490 -> 134: OK!
135 -> 0.529412 -> 135: OK!
136 -> 0.533333 -> 136: OK!
137 -> 0.537255 -> 137: OK!
138 -> 0.541176 -> 138: OK!
139 -> 0.545098 -> 139: OK!
140 -> 0.549020 -> 140: OK!
141 -> 0.552941 -> 141: OK!
142 -> 0.556863 -> 142: OK!
143 -> 0.560784 -> 143: OK!
144 -> 0.564706 -> 144: OK!
145 -> 0.568627 -> 145: OK!
146 -> 0.572549 -> 146: OK!
147 -> 0.576471 -> 147: OK!
148 -> 0.580392 -> 148: OK!
149 -> 0.584314 -> 149: OK!
150 -> 0.588235 -> 150: OK!
151 -> 0.592157 -> 151: OK!
152 -> 0.596078 -> 152: OK!
153 -> 0.600000 -> 153: OK!
154 -> 0.603922 -> 154: OK!
155 -> 0.607843 -> 155: OK!
156 -> 0.611765 -> 156: OK!
157 -> 0.615686 -> 157: OK!
158 -> 0.619608 -> 158: OK!
159 -> 0.623529 -> 159: OK!
160 -> 0.627451 -> 160: OK!
161 -> 0.631373 -> 161: OK!
162 -> 0.635294 -> 162: OK!
163 -> 0.639216 -> 163: OK!
164 -> 0.643137 -> 164: OK!
165 -> 0.647059 -> 165: OK!
166 -> 0.650980 -> 166: OK!
167 -> 0.654902 -> 167: OK!
168 -> 0.658824 -> 168: OK!
169 -> 0.662745 -> 169: OK!
170 -> 0.666667 -> 170: OK!
171 -> 0.670588 -> 171: OK!
172 -> 0.674510 -> 172: OK!
173 -> 0.678431 -> 173: OK!
174 -> 0.682353 -> 174: OK!
175 -> 0.686275 -> 175: OK!
176 -> 0.690196 -> 176: OK!
177 -> 0.694118 -> 177: OK!
178 -> 0.698039 -> 178: OK!
179 -> 0.701961 -> 179: OK!
180 -> 0.705882 -> 180: OK!
181 -> 0.709804 -> 181: OK!
182 -> 0.713726 -> 182: OK!
183 -> 0.717647 -> 183: OK!
184 -> 0.721569 -> 184: OK!
185 -> 0.725490 -> 185: OK!
186 -> 0.729412 -> 186: OK!
187 -> 0.733333 -> 187: OK!
188 -> 0.737255 -> 188: OK!
189 -> 0.741176 -> 189: OK!
190 -> 0.745098 -> 190: OK!
191 -> 0.749020 -> 191: OK!
192 -> 0.752941 -> 192: OK!
193 -> 0.756863 -> 193: OK!
194 -> 0.760784 -> 194: OK!
195 -> 0.764706 -> 195: OK!
196 -> 0.768627 -> 196: OK!
197 -> 0.772549 -> 197: OK!
198 -> 0.776471 -> 198: OK!
199 -> 0.780392 -> 199: OK!
200 -> 0.784314 -> 200: OK!
201 -> 0.788235 -> 201: OK!
202 -> 0.792157 -> 202: OK!
203 -> 0.796078 -> 203: OK!
204 -> 0.800000 -> 204: OK!
205 -> 0.803922 -> 205: OK!
206 -> 0.807843 -> 206: OK!
207 -> 0.811765 -> 207: OK!
208 -> 0.815686 -> 208: OK!
209 -> 0.819608 -> 209: OK!
210 -> 0.823529 -> 210: OK!
211 -> 0.827451 -> 211: OK!
212 -> 0.831373 -> 212: OK!
213 -> 0.835294 -> 213: OK!
214 -> 0.839216 -> 214: OK!
215 -> 0.843137 -> 215: OK!
216 -> 0.847059 -> 216: OK!
217 -> 0.850980 -> 217: OK!
218 -> 0.854902 -> 218: OK!
219 -> 0.858824 -> 219: OK!
220 -> 0.862745 -> 220: OK!
221 -> 0.866667 -> 221: OK!
222 -> 0.870588 -> 222: OK!
223 -> 0.874510 -> 223: OK!
224 -> 0.878431 -> 224: OK!
225 -> 0.882353 -> 225: OK!
226 -> 0.886275 -> 226: OK!
227 -> 0.890196 -> 227: OK!
228 -> 0.894118 -> 228: OK!
229 -> 0.898039 -> 229: OK!
230 -> 0.901961 -> 230: OK!
231 -> 0.905882 -> 231: OK!
232 -> 0.909804 -> 232: OK!
233 -> 0.913725 -> 233: OK!
234 -> 0.917647 -> 234: OK!
235 -> 0.921569 -> 235: OK!
236 -> 0.925490 -> 236: OK!
237 -> 0.929412 -> 237: OK!
238 -> 0.933333 -> 238: OK!
239 -> 0.937255 -> 239: OK!
240 -> 0.941176 -> 240: OK!
241 -> 0.945098 -> 241: OK!
242 -> 0.949020 -> 242: OK!
243 -> 0.952941 -> 243: OK!
244 -> 0.956863 -> 244: OK!
245 -> 0.960784 -> 245: OK!
246 -> 0.964706 -> 246: OK!
247 -> 0.968627 -> 247: OK!
248 -> 0.972549 -> 248: OK!
249 -> 0.976471 -> 249: OK!
250 -> 0.980392 -> 250: OK!
251 -> 0.984314 -> 251: OK!
252 -> 0.988235 -> 252: OK!
253 -> 0.992157 -> 253: OK!
254 -> 0.996078 -> 254: OK!
255 -> 1.000000 -> 255: OK!