Repair this code

Repair safe_div so it divides a by b only after both illegal divisions have been ruled out, writing the quotient through out when the division is legal.

Steps

• a and b are any int. out always points to one writable int.
• When the division is legal, store a / b in *out and return 0.
• When it is not legal, return -1 and leave *out holding whatever the caller put there. No partial write and no sentinel of your own.
• Two divisions are illegal, not one. b == 0 is the case everyone guards. The other is a == INT_MIN with b == -1: the mathematical quotient is 2147483648, one past INT_MAX, so the result is not representable and the operation is undefined. On x86 the CPU raises the same hardware fault as a division by zero, and the process dies.
• Rule out both cases before the / runs. Testing after the division buys you nothing, since the division is what kills the program.
• Integer division in C truncates toward zero. It does not round and it does not floor: 7 / 2 is 3, -7 / 2 is -3, 7 / -2 is -3, and -1 / 2 is 0.
• Every other pair is legal, including the ones that look dangerous: INT_MIN / 1 is -2147483648, INT_MIN / -2 is 1073741824, and INT_MAX / -1 is -2147483647.
• INT_MIN comes from <limits.h>. You may call nothing.
• The starter compiles without a single diagnostic and passes most of the tests. Its fault is invisible to the compiler and only surfaces at run time, on the case it fails to check.
• The tests print ret= then your return value, then out= then the value of *out, on one line. *out is printed after a failure too, seeded with a sentinel, so a write on the failure path is caught.

Repair this code

Repair safe_div so it divides a by b only after both illegal divisions have been ruled out, writing the quotient through out when the division is legal.

Steps

• a and b are any int. out always points to one writable int.
• When the division is legal, store a / b in *out and return 0.
• When it is not legal, return -1 and leave *out holding whatever the caller put there. No partial write and no sentinel of your own.
• Two divisions are illegal, not one. b == 0 is the case everyone guards. The other is a == INT_MIN with b == -1: the mathematical quotient is 2147483648, one past INT_MAX, so the result is not representable and the operation is undefined. On x86 the CPU raises the same hardware fault as a division by zero, and the process dies.
• Rule out both cases before the / runs. Testing after the division buys you nothing, since the division is what kills the program.
• Integer division in C truncates toward zero. It does not round and it does not floor: 7 / 2 is 3, -7 / 2 is -3, 7 / -2 is -3, and -1 / 2 is 0.
• Every other pair is legal, including the ones that look dangerous: INT_MIN / 1 is -2147483648, INT_MIN / -2 is 1073741824, and INT_MAX / -1 is -2147483647.
• INT_MIN comes from <limits.h>. You may call nothing.
• The starter compiles without a single diagnostic and passes most of the tests. Its fault is invisible to the compiler and only surfaces at run time, on the case it fails to check.
• The tests print ret= then your return value, then out= then the value of *out, on one line. *out is printed after a failure too, seeded with a sentinel, so a write on the failure path is caught.