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+/*
+ * Example Gen3-multiboot payload by slipstream/RoL 2017.
+ *
+ * This software may be modified and distributed under the terms
+ * of the MIT license.  See the LICENSE file for details.
+ *
+ * libpayload.c: contains helper functions for the payload
+ */
+ 
+#include <gba.h>
+#include "payload.h"
+
+// private functions
+static void CryptBoxPokemon(struct BoxPokemon* pkm);
+static u16 crc16(const u8* data, u16 len);
+static u32 CalculateRamScriptDataChecksum(struct RamScriptData* ramScript);
+
+/**
+ * Decrypts the substructures of a Pokémon structure, so they can be viewed or modified easily.
+ * Remember to call EncryptPokemon() afterwards.
+ * @param struct Pokemon* pkm The Pokémon to decrypt the substructures of.
+*/
+void DecryptPokemon(struct Pokemon* pkm) {
+        struct BoxPokemon* boxMon = &(pkm->box);
+        CryptBoxPokemon(boxMon);
+}
+
+/**
+ * Private function that does the actual work of crypting the substructures of a BoxPokemon.
+ * @param struct BoxPokemon* pkm The BoxPokemon whose substructures will be crypted.
+*/
+static void CryptBoxPokemon(struct BoxPokemon* pkm) {
+        for (u32 i = 0; i < 12; i++) {
+                pkm->secure.raw[i] ^= (pkm->otId ^ pkm->personality);
+        }
+}
+
+/**
+ * Decrypts the substructures of a core Pokémon structure, so they can be viewed or modified easily.
+ * Used by DecryptPokemon().
+ * Remember to call EncryptPokemon() afterwards.
+ * @param struct BoxPokemon* pkm The BoxPokemon to decrypt the substructures of.
+*/
+void DecryptBoxPokemon(struct BoxPokemon* pkm) {
+        CryptBoxPokemon(pkm);
+}
+
+/**
+ * Encrypts the substructures of a Pokémon structure, and fixes the checksum.
+ * Must be used after DecryptPokemon() has been called, otherwise the Pokémon you decrypted and forgot to re-encrypt will become a Bad Egg.
+ * @param struct Pokemon* pkm The Pokémon to encrypt the substructures and fix the checksum of.
+*/
+void EncryptPokemon(struct Pokemon* pkm) {
+        struct BoxPokemon* boxMon = &(pkm->box);
+        EncryptBoxPokemon(boxMon);
+}
+
+/**
+ * Encrypts the substructures of a core Pokémon structure, and fixes the checksum.
+ * Must be used after DecryptBoxPokemon() has been called, otherwise the Pokémon you decrypted and forgot to re-encrypt will become a Bad Egg.
+ * @param struct BoxPokemon* pkm The BoxPokemon to encrypt the substructures and fix the checksum of.
+*/
+void EncryptBoxPokemon(struct BoxPokemon* pkm) {
+        FixBoxPokemonChecksum(pkm);
+        CryptBoxPokemon(pkm);
+}
+
+/**
+ * Gets a substructure of a Pokémon structure.
+ * Call DecryptPokemon() first or the substructure data will be encrypted.
+ * @param struct Pokemon* pkm The Pokemon to get a substructure of.
+ * @param u8 substructId The substructure to get.
+ * @return union PokemonSubstruct* The substructure.
+*/
+union PokemonSubstruct* GetPokemonSubstruct(struct Pokemon* pkm,u8 substructId) {
+        struct BoxPokemon* boxMon = &(pkm->box);
+        return GetBoxPokemonSubstruct(boxMon,substructId);
+}
+
+/**
+ * Gets a substructure of a core Pokémon structure.
+ * Call DecryptBoxPokemon() first or the substructure data will be encrypted.
+ * @param struct Pokemon* pkm The Pokemon to get a substructure of.
+ * @param u8 substructId The substructure to get.
+ * @return union PokemonSubstruct* The substructure.
+*/
+union PokemonSubstruct* GetBoxPokemonSubstruct(struct BoxPokemon* pkm,u8 substructId) {
+        if (substructId > 3) return NULL;
+        u32 personality = pkm->personality;
+        // Staring at the substruct indexes, I noticed the last two columns are the reverse of the first two!
+        // that is, substructId==2 column is the reverse of substructId==1, substructId==3 is the reverse of substructId==0
+        // At least that means there's no need to hardcode all four.
+        u8 substruct_idxes[2][24] = {
+                { 0, 0, 0, 0, 0, 0, 1, 1, 2, 3, 2, 3, 1, 1, 2, 3, 2, 3, 1, 1, 2, 3, 2, 3 },
+                { 1, 1, 2, 3, 2, 3, 0, 0, 0, 0, 0, 0, 2, 3, 1, 1, 3, 2, 2, 3, 1, 1, 3, 2 }
+        };
+        u32 modulo = (personality % 24);
+        if (substructId < 2) {
+                return &( pkm->secure.substructs[ substruct_idxes[substructId][modulo] ] );
+        }
+        return &( pkm->secure.substructs[ substruct_idxes[3 - substructId][23 - modulo] ] );
+}
+
+/**
+ * Gets the checksum of a core Pokémon structure.
+ * @param struct BoxPokemon* pkm The BoxPokemon to calculate the checksum of.
+ * @return u16 The checksum.
+*/
+u16 CalculateBoxPokemonChecksum(struct BoxPokemon* pkm) {
+        u16 checksum = 0;
+        union PokemonSubstruct* substructs[4] = {
+                GetBoxPokemonSubstruct(pkm,0),
+                GetBoxPokemonSubstruct(pkm,1),
+                GetBoxPokemonSubstruct(pkm,2),
+                GetBoxPokemonSubstruct(pkm,3)
+        };
+        
+        for (int substruct = 0; substruct < 4; substruct++) {
+                for (int i = 0; i < 6; i++) {
+                        checksum += substructs[substruct]->raw[i];
+                }
+        }
+        return checksum;
+}
+
+/**
+ * Fixes the checksum of a core Pokémon structure.
+ * @param struct BoxPokemon* pkm The BoxPokemon to fix the checksum of.
+*/
+void FixBoxPokemonChecksum(struct BoxPokemon* pkm) {
+        pkm->checksum = CalculateBoxPokemonChecksum(pkm);
+}
+
+/**
+ * Gets the zeroth substructure ("Growth") of a Pokémon structure.
+ * Call DecryptPokemon() first or the substructure data will be encrypted.
+ * @param struct Pokemon* pkm The Pokémon to get a substructure of.
+ * @return struct PokemonSubstruct0* The substructure.
+*/
+struct PokemonSubstruct0* GetPokemonSubstruct0(struct Pokemon* pkm) {
+        struct BoxPokemon* boxMon = &(pkm->box);
+        return GetBoxPokemonSubstruct0(boxMon);
+}
+
+/**
+ * Gets the zeroth substructure ("Growth") of a core Pokémon structure.
+ * Call DecryptBoxPokemon() first or the substructure data will be encrypted.
+ * @param struct BoxPokemon* pkm The BoxPokemon to get the substructure of.
+ * @return struct PokemonSubstruct0* The substructure.
+*/
+struct PokemonSubstruct0* GetBoxPokemonSubstruct0(struct BoxPokemon* pkm) {
+        return &( GetBoxPokemonSubstruct(pkm,0)->type0 );
+}
+
+/**
+ * Gets the first substructure ("Attacks") of a Pokémon structure.
+ * Call DecryptPokemon() first or the substructure data will be encrypted.
+ * @param struct Pokemon* pkm The Pokémon to get a substructure of.
+ * @return struct PokemonSubstruct0* The substructure.
+*/
+struct PokemonSubstruct1* GetPokemonSubstruct1(struct Pokemon* pkm) {
+        struct BoxPokemon* boxMon = &(pkm->box);
+        return GetBoxPokemonSubstruct1(boxMon);
+}
+
+/**
+ * Gets the first substructure ("Attacks") of a core Pokémon structure.
+ * Call DecryptBoxPokemon()  first or the substructure data will be encrypted.
+ * @param struct BoxPokemon* pkm The BoxPokemon to get the substructure of.
+ * @return struct PokemonSubstruct1* The substructure.
+*/
+struct PokemonSubstruct1* GetBoxPokemonSubstruct1(struct BoxPokemon* pkm) {
+        return &( GetBoxPokemonSubstruct(pkm,1)->type1 );
+}
+
+/**
+ * Gets the second substructure ("EVs & Condition") of a Pokémon structure.
+ * Call DecryptPokemon() first or the substructure data will be encrypted.
+ * @param struct Pokemon* pkm The Pokémon to get a substructure of.
+ * @return struct PokemonSubstruct0* The substructure.
+*/
+struct PokemonSubstruct2* GetPokemonSubstruct2(struct Pokemon* pkm) {
+        struct BoxPokemon* boxMon = &(pkm->box);
+        return GetBoxPokemonSubstruct2(boxMon);
+}
+
+/**
+ * Gets the second substructure ("EVs & Condition") of a core Pokémon structure.
+ * Call DecryptBoxPokemon()  first or the substructure data will be encrypted.
+ * @param struct BoxPokemon* pkm The BoxPokemon to get the substructure of.
+ * @return struct PokemonSubstruct2* The substructure.
+*/
+struct PokemonSubstruct2* GetBoxPokemonSubstruct2(struct BoxPokemon* pkm) {
+        return &( GetBoxPokemonSubstruct(pkm,2)->type2 );
+}
+
+/**
+ * Gets the third substructure ("Miscellaneous")  of a Pokémon structure.
+ * Call DecryptPokemon() first or the substructure data will be encrypted.
+ * @param struct Pokemon* pkm The Pokémon to get a substructure of.
+ * @return struct PokemonSubstruct0* The substructure.
+*/
+struct PokemonSubstruct3* GetPokemonSubstruct3(struct Pokemon* pkm) {
+        struct BoxPokemon* boxMon = &(pkm->box);
+        return GetBoxPokemonSubstruct3(boxMon);
+}
+
+/**
+ * Gets the third substructure ("Miscellaneous") of a core Pokémon structure.
+ * Call DecryptBoxPokemon()  first or the substructure data will be encrypted.
+ * @param struct BoxPokemon* pkm The BoxPokemon to get the substructure of.
+ * @return struct PokemonSubstruct3* The substructure.
+*/
+struct PokemonSubstruct3* GetBoxPokemonSubstruct3(struct BoxPokemon* pkm) {
+        return &( GetBoxPokemonSubstruct(pkm,3)->type3 );
+}
+
+/**
+ * Calculates the checksum for an R/S-specific Enigma Berry structure in SaveBlock1.
+ * @param struct EnigmaBerry* enigmaBerry The R/S-specific Enigma Berry to calculate the checksum for.
+ * @return u32 The checksum.
+*/
+u32 CalculateEnigmaBerryChecksumRS(struct EnigmaBerry* enigmaBerry) {
+        if (!GAME_RS) return 0; // Enigma Berry structure changed in FR/LG, use CalculateEnigmaBerryChecksumFRLGE() instead.
+        u32 checksum = 0;
+        // Save off and zero out the original Enigma Berry description pointers.
+        const u8* description[2] = { enigmaBerry->berry.description1, enigmaBerry->berry.description2 };
+        enigmaBerry->berry.description1 = enigmaBerry->berry.description2 = NULL;
+        u8* enigmaBerryBytes = (u8*)enigmaBerry;
+        // Calculate the checksum.
+        for (u32 i = 0; i < 1324; i++) {
+                checksum += enigmaBerryBytes[i];
+        }
+        // Restore the saved description.
+        enigmaBerry->berry.description1 = description[0];
+        enigmaBerry->berry.description2 = description[1];
+        return checksum;
+}
+
+/**
+ * Calculates the checksum for an FR/LG/Emerald-specific Enigma Berry structure in SaveBlock1.
+ * @param struct EnigmaBerryFRLGE* enigmaBerry The FR/LG/Emerald-specific Enigma Berry to calculate the checksum for.
+ * @return u32 The checksum.
+*/
+u32 CalculateEnigmaBerryChecksumFRLGE(struct EnigmaBerryFRLGE* enigmaBerry) {
+        if (GAME_RS) return 0; // Enigma Berry structure is different in R/S, use CalculateEnigmaBerryChecksumRS() instead.
+        u32 checksum = 0;
+        u8* enigmaBerryBytes = (u8*)enigmaBerry;
+        for (int i = 0; i < 0x30; i++) {
+                checksum += enigmaBerryBytes[i];
+        }
+        return checksum;
+}
+
+/**
+ * Calculates the checksum for an unspecified Enigma Berry structure in SaveBlock1. (detected by current game)
+ * @param void* enigmaBerry The Enigma Berry structure to calculate the checksum for.
+ * @return u32 The checksum.
+ */
+u32 CalculateEnigmaBerryChecksum(void* enigmaBerry) {
+        if (GAME_RS) return CalculateEnigmaBerryChecksumRS( (struct EnigmaBerry*) enigmaBerry );
+        return CalculateEnigmaBerryChecksumFRLGE( (struct EnigmaBerryFRLGE*) enigmaBerry );
+}
+
+/**
+ * Calculates the checksum for a RAM script structure in SaveBlock1.
+ * @param struct RamScript* ramScript The RAM script structure to calculate the checksum for.
+ * @return u32 The checksum.
+ */
+u32 CalculateRamScriptChecksum(struct RamScript* ramScript) {
+        asm(""); // make sure the call to CalculateRamScriptDataChecksum() is *not* inlined.
+        // For some reason, if it gets inlined, something happens, and the wrong length is used when checksumming...
+        return CalculateRamScriptDataChecksum(&ramScript->data);
+}
+
+/**
+ * Calculates the checksum for a RAM script structure in SaveBlock1.
+ * @param struct RamScript* ramScript The RAM script structure to calculate the checksum for.
+ * @return u32 The checksum.
+ */
+static __attribute__ ((noinline)) u32 CalculateRamScriptDataChecksum(struct RamScriptData* ramScript) {
+        u32 checksum = 0;
+        u32 i = 0;
+        u8* ramScriptBytes = (u8*)(ramScript);
+        if (GAME_RS) {
+                for (i = 0; i < sizeof(struct RamScriptData); i++) checksum += ramScriptBytes[i];
+                return checksum;
+        }
+        
+        return (u32)crc16(ramScriptBytes,sizeof(struct RamScriptData) + 1);
+}
+
+/**
+ * Private function to CRC-16, (used by FR/LG/Emerald ramscript checksum). Adapted from http://forums.glitchcity.info/index.php?topic=7114.0
+ * @param u8* Data to checksum
+ * @param u16 Length of data
+ * @return u16 The checksum
+*/
+static u16 crc16(const u8* data, u16 len) {
+        u16 crc = 0x1121;
+        for (u16 i = 0; i < len; ++i) {
+                crc ^= data[i];
+                for (u16 j = 0; j < 8; ++j) {
+                        if(crc & 1) {
+                                crc = (crc >> 1) ^ 0x8408;
+                        } else {
+                                crc >>= 1;
+                        }
+                }
+        }
+        return ~crc;
+}
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