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Simplify RBY checksum calc

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utilize unchecked byte overflow
remove unnecessary zeroing -- t's immediately after the checksummed
region. even if it was included, chk += 0 is still 0.
This commit is contained in:
Kurt 2018-07-21 19:24:09 -07:00
parent 0c5c9bc33c
commit da839988af
1 changed files with 14 additions and 27 deletions
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41
PKHeX.Core/Saves/SAV1.cs
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@ -205,35 +205,22 @@ protected override byte[] Write(bool DSV)
public override bool IsPKMPresent(int Offset) => PKX.IsPKMPresentGB(Data, Offset);
// Checksums
protected override void SetChecksums()
{
int CHECKSUM_OFS = Japanese ? 0x3594 : 0x3523;
Data[CHECKSUM_OFS] = 0;
uint chksum = 0;
for (int i = 0x2598; i < CHECKSUM_OFS; i++)
{
chksum += Data[i];
}
chksum = ~chksum;
chksum &= 0xFF;
Data[CHECKSUM_OFS] = (byte)chksum;
}
public override bool ChecksumsValid
{
get
{
int CHECKSUM_OFS = Japanese ? 0x3594 : 0x3523;
byte temp = Data[CHECKSUM_OFS]; // cache current chk
SetChecksums(); // chksum is recalculated (after being set to 0 to perform check)
byte chk = Data[CHECKSUM_OFS]; // correct checksum
Data[CHECKSUM_OFS] = temp; // restore old chk
return temp == chk;
}
}
protected override void SetChecksums() => Data[CHECKSUM_OFS] = GetRBYChecksum(CHECKSUM_OFS);
public override bool ChecksumsValid => Data[CHECKSUM_OFS] == GetRBYChecksum(CHECKSUM_OFS);
public override string ChecksumInfo => ChecksumsValid ? "Checksum valid." : "Checksum invalid";
private const int CHECKSUM_START = 0x2598;
private int CHECKSUM_OFS => Japanese ? 0x3594 : 0x3523;
private byte GetRBYChecksum(int end)
{
byte chksum = 0;
for (int i = CHECKSUM_START; i < end; i++)
chksum += Data[i];
chksum ^= 0xFF;
return chksum;
}
// Trainer Info
public override GameVersion Version { get; protected set; }