Erroneous outputs while running checksum C code

./corrupt_data "Star Platinum, Za Warudooo!"
Before corruption       : 53 74 61 72 20 50 6C 61 74 69 6E 75 6D 2C 20 5A 61 20 57 61 72 75 64 6F 6F 6F 21 ..

After corruption        : 53 74 61 72 20 50 6C 61 74 69 6E 75 6D 2C 20 5A FFFFFFE1 20 57 61 72 75 64 6F 6F 6F 21 ..
Corrupted parts         : .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. FFFFFF80 .. .. .. .. .. .. .. .. .. .. ..

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Result                  : String is corrupted

./corrupt_data "Star Platinum, Za Warudooo!"
Before corruption       : 53 74 61 72 20 50 6C 61 74 69 6E 75 6D 2C 20 5A 61 20 57 61 72 75 64 6F 6F 6F 21 ..

After corruption        : 53 74 61 72 20 50 6C 61 74 69 6E 75 6D 2C 20 5A 61 20 57 61 72 75 64 6F 6F FFFFFFEF 21 ..
Corrupted parts         : .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. FFFFFF80 .. ..

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Result                  : String is corrupted

./corrupt_data "Star Platinum, Za Warudooo!"
Before corruption       : 53 74 61 72 20 50 6C 61 74 69 6E 75 6D 2C 20 5A 61 20 57 61 72 75 64 6F 6F 6F 21 ..

After corruption        : 53 74 61 72 20 50 6C 61 74 69 6E 75 6D 2C 20 5A 61 20 57 61 72 75 64 FFFFFFEF 6F 6F 21 ..
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Corrupted parts         : .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. FFFFFF80 .. .. .. ..

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Result                  : String is corrupted

./corrupt_data "Star Platinum, Za Warudooo!"
Before corruption       : 53 74 61 72 20 50 6C 61 74 69 6E 75 6D 2C 20 5A 61 20 57 61 72 75 64 6F 6F 6F 21 ..

After corruption        : 53 74 61 72 20 50 6C 61 74 69 6E 75 6D 2C 20 5A 61 20 57 61 72 FFFFFFF5 64 6F 6F 6F 21 ..
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Corrupted parts         : .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. FFFFFF80 .. .. .. .. .. ..

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Result                  : String is corrupted