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The examples here fall under the exception MSC17-C-EX2 in MSC17-C. Finish every set of statements associated with a case label with a break statement.

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When i = 1, the entire for loop is executed. When i = 2, two increments to j are made before the loop starts. When i = 3, one increment to j is made before the loop starts. The default case is no loop. Consequently, the function has the following behavior:

Compliant

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Solution

The compliant example solution separates the switch and for blocks:

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Many people . . . have said that the worst feature of C is that switches don't break automatically before each case label. This code forms some sort of argument in that debate, but I'm not sure whether it's for or against.

Compliant

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Solution (Duff's Device)

This is an alternative implementation of Duff's device, which separates the switch statement and loop:

int n = (count + 7) / 8;
switch (count % 8) {
  case 0: *to = *from++; /* Fall through */
  case 7: *to = *from++; /* Fall through */
  case 6: *to = *from++; /* Fall through */
  case 5: *to = *from++; /* Fall through */
  case 4: *to = *from++; /* Fall through */
  case 3: *to = *from++; /* Fall through */
  case 2: *to = *from++; /* Fall through */
  case 1: *to = *from++; /* Fall through */
}
while (--n > 0) {
  *to = *from++;
  *to = *from++;
  *to = *from++;
  *to = *from++;
  *to = *from++;
  *to = *from++;
  *to = *from++;
  *to = *from++;
}

Risk Assessment

Automated Detection

Related Guidelines

Bibliography

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