Routines
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C058: Handler: User Pressed "ENTER"
Used by the routine at Handler_UserInput.
Parses and tokenises the user's command input when they press ENTER. The input is broken down into individual words, each word is looked up in the vocabulary table, and unrecognised words are reported to the player.
Input
HL Current position in the command buffer
A Which contains 0D ("ENTER") at this point.
UserInput_Enter C058 LD (HL),A Write 0D to the command buffer at the current position for use as a termination character.
Force a newline to be "printed" to the screen.
C059 CALL SwitchNormalScreenOutput Call SwitchNormalScreenOutput.
C05C CALL PrintCharacter Call PrintCharacter.
Initialise the word token buffer. This buffer will store up to 0A vocabulary tokens (one per word in the command). Each token is the index of the word in the vocabulary table.
C05F LD HL,$BD66 HL=UserInput_FirstToken.
C062 LD A,$FF A=FF.
C064 LD B,$0A Set a counter in B for the size of the word token buffer (0A bytes).
Fill the word token buffer with FF (the terminator value) to mark all slots as empty.
EmptyWordTokenBuffer_Loop C066 LD (HL),A Write A to *HL.
C067 INC HL Increment HL by one.
C068 DJNZ EmptyWordTokenBuffer_Loop Decrease the word token buffer counter by one and loop back to EmptyWordTokenBuffer_Loop until the whole buffer is cleared.
C06A LD HL,$BD34 HL=CommandBuffer.
C06D LD C,$0A C=0A.
Begin parsing the command. Extract each word from the input, look it up in the vocabulary, and store its token. Words are separated by spaces or commas, and the word "The" is automatically ignored.
UserInputParser_Loop C06F LD DE,$BD71 DE=FourLetterBuffer.
C072 LD B,$04 Set a counter in B for the 04 letters.
Clear the four-letter buffer to spaces so a short word cannot match the previous one's tail.
C074 LD A,$20 A=20.
ClearWordBuffer_Loop C076 LD (DE),A Write a space character (20) to the buffer.
C077 INC DE Move to the next letter.
C078 DJNZ ClearWordBuffer_Loop Decrease the counter by one and loop back to ClearWordBuffer_Loop until the counter is zero.
C07A XOR A A=00.
C07B OR C A|=C.
C07C JP Z,CheckIfEmptyInput Jump to CheckIfEmptyInput if DE is equal to C.
C07F LD A,(HL) Jump to CheckIfEmptyInput if *HL is equal to 0D.
C080 CP $0D
C082 JP Z,CheckIfEmptyInput
C085 LD B,$04 B=04.
C087 LD DE,$BD71 DE=FourLetterBuffer.
Extract the next word from the command buffer. Copy up to 04 characters (the maximum word length) into the word buffer, stopping at a space, comma, or end of input.
CopyWord_Loop C08A LD A,(HL) Read the character from *HL and store it in A.
C08B CP $0D Jump to CheckIfThe if this character is a newline (0D, end of input).
C08D JR Z,CheckIfThe
C08F CP $20 Jump to SkipDelimiters_Loop if the character is either an ASCII "SPACE" (20) or an ASCII comma (2C).
C091 JR Z,SkipDelimiters_Loop
C093 CP $2C
C095 JR Z,SkipDelimiters_Loop
C097 LD (DE),A Write this character to the word buffer at *DE.
C098 INC HL Move to the next character in the command buffer.
C099 INC DE Move to the next position in the word buffer.
C09A DJNZ CopyWord_Loop Decrease counter by one and loop back to CopyWord_Loop until counter is zero.
If the word was longer than 04 characters, skip over the remaining characters until a delimiter (space, comma, or end of input) is found.
SkipRemainingWord_Loop C09C LD A,(HL) Read the character from *HL and store it in A.
C09D CP $0D Jump to CheckIfThe if this character is a newline (0D).
C09F JR Z,CheckIfThe
C0A1 CP $20 Jump to SkipDelimiters_Loop if the character is an ASCII "SPACE" (20).
C0A3 JR Z,SkipDelimiters_Loop
C0A5 CP $2C Jump to SkipDelimiters_Loop if the character is an ASCII comma (2C).
C0A7 JR Z,SkipDelimiters_Loop
C0A9 INC HL Move to the next character in the command buffer.
C0AA JR SkipRemainingWord_Loop Jump to SkipRemainingWord_Loop.
Skip over any consecutive spaces or commas to find the start of the next word.
SkipDelimiters_Loop C0AC INC HL Move to the next character in the command buffer.
C0AD LD A,(HL) Read the character from *HL and store it in A.
C0AE CP $20 Jump to SkipDelimiters_Loop if the character is an ASCII "SPACE" (20).
C0B0 JR Z,SkipDelimiters_Loop
C0B2 CP $2C Jump to SkipDelimiters_Loop if the character is an ASCII comma (2C).
C0B4 JR Z,SkipDelimiters_Loop
Check if the extracted word is "The". If it is, ignore it and continue with the next word (adventure games typically ignore articles like "the", "a", "an").
Preserve the command pointer, word buffer and token counter while comparing.
CheckIfThe C0B6 PUSH HL Stash HL, DE and BC on the stack.
C0B7 PUSH DE
C0B8 PUSH BC
C0B9 LD HL,$BD8C HL=Messaging_The.
C0BC LD DE,$BD71 DE=FourLetterBuffer.
C0BF LD B,$04 B=04.
CompareWord_Loop C0C1 LD A,(DE) Jump to AfterCompareWord if the characters don't match (the word is not "The").
C0C2 CP (HL)
C0C3 JR NZ,AfterCompareWord
C0C5 INC DE Move to the next character in the extracted word.
C0C6 INC HL Move to the next character in "The".
C0C7 DJNZ CompareWord_Loop Decrease counter by one and loop back to CompareWord_Loop until all 04 characters have been compared.
Restore the registers saved before the "THE" comparison.
AfterCompareWord C0C9 POP BC Restore BC, DE and HL from the stack.
C0CA POP DE
C0CB POP HL
C0CC JR Z,UserInputParser_Loop Jump to UserInputParser_Loop if the words matched (this was "The", so skip it and process the next word).
C0CE DEC C Decrease C by one.
C0CF LD ($BD7D),HL Write HL to *TempStore_TablePointer.
C0D2 LD ($BD7F),DE Write DE to *TempStore_TableIndex.
C0D6 LD ($BD81),BC Write BC to *TempStore_WordCount.
Look up the word in the vocabulary table. The vocabulary contains all recognised verbs, nouns, and other words the game understands. Each entry can have synonyms separated by commas.
C0DA LD HL,($BD0C) HL=*Pointer_Vocabulary.
C0DD LD C,$00 Set the token number in C to 00.
VocabularyLookup_Loop C0DF LD A,(HL) Jump to ProcessUnrecognisedWords if the word is the FF terminator.
C0E0 CP $FF
C0E2 JR Z,ProcessUnrecognisedWords
CompareVocabularyWord C0E4 LD DE,$BD71 DE=FourLetterBuffer.
C0E7 LD B,$04 Set a counter in B for the 04 letters.
CompareVocabularyWord_Loop C0E9 LD A,(DE) Jump to VocabularyWordNoMatch if this letter does not match.
C0EA CP (HL)
C0EB JR NZ,VocabularyWordNoMatch
C0ED INC DE Move to the next letter of the four-letter buffer.
C0EE INC HL Move to the next vocabulary letter.
C0EF DJNZ CompareVocabularyWord_Loop Decrease the letter counter by one and loop back to CompareVocabularyWord_Loop until the counter is zero.
The word matched. Calculate which token-buffer slot to use and store the vocabulary index as the token.
C0F1 LD HL,$BD81 HL=TempStore_WordCount.
C0F4 LD A,$09 A=09.
C0F6 SUB (HL) Calculate the token buffer slot index: A-=*HL.
C0F7 LD D,$00 Turn the slot index into a 16-bit offset in DE.
C0F9 LD E,A
C0FA LD HL,$BD66 Calculate the address of the token buffer slot: HL=UserInput_FirstToken+DE.
C0FD ADD HL,DE
C0FE LD (HL),C Store the vocabulary index (C) in the token buffer slot.
C0FF LD HL,($BD7D) Restore the command buffer position from *TempStore_TablePointer.
C102 LD DE,($BD7F) Restore the word buffer position from *TempStore_TableIndex.
C106 LD BC,($BD81) Restore the word counter from *TempStore_WordCount.
C10A JP UserInputParser_Loop Jump to UserInputParser_Loop.
This vocabulary word did not match. Step past the remaining letters. A comma keeps the same token for a synonym; anything else advances the token number for the next entry.
VocabularyWordNoMatch C10D LD E,B Turn the remaining letter count into a 16-bit offset in DE.
C10E LD D,$00
C110 ADD HL,DE Move HL past the unmatched letters.
C111 LD A,(HL) Fetch the next vocabulary byte into A.
C112 CP $2C Jump to VocabularyNextEntry if this byte is not a comma (2C).
C114 JR NZ,VocabularyNextEntry
C116 INC HL Move past the comma.
C117 JR CompareVocabularyWord Jump to CompareVocabularyWord to try matching the synonym.
VocabularyNextEntry C119 INC C Advance the token number for the next vocabulary entry.
C11A JR VocabularyLookup_Loop Jump to VocabularyLookup_Loop.
All recognised words have been tokenised. Now check if there are any unrecognised words remaining in the input. If so, display an error message to the player showing which word(s) weren't understood.
ProcessUnrecognisedWords C11C LD HL,($BD7D) HL=*TempStore_TablePointer.
C11F LD DE,($BD7F) DE=*TempStore_TableIndex.
C123 LD BC,($BD81) BC=*TempStore_WordCount.
C127 LD A,$0A C=0A-C.
C129 SUB C
C12A LD C,A
C12B LD HL,$BD34 HL=CommandBuffer.
ProcessUnrecognisedWords_Loop C12E DEC C Decrease C by one.
C12F JR Z,PrintUnrecognisedWord Jump to PrintUnrecognisedWord if C is equal to 0A (no unrecognised words found).
FindUnrecognisedWord_Loop C131 LD A,(HL) Read the character from *HL and store it in A.
C132 CP $20 Jump to SkipDelimiters_Loop2 if the character is an ASCII "SPACE" (20).
C134 JR Z,SkipDelimiters_Loop2
C136 CP $2C Jump to SkipDelimiters_Loop2 if the character is an ASCII comma (2C).
C138 JR Z,SkipDelimiters_Loop2
C13A INC HL Move to the next character in the command buffer.
C13B JR FindUnrecognisedWord_Loop Jump to FindUnrecognisedWord_Loop.
SkipDelimiters_Loop2 C13D INC HL Move to the next character in the command buffer.
C13E LD A,(HL) Read the character from *HL and store it in A.
C13F CP $20 Jump to SkipDelimiters_Loop2 if the character is an ASCII "SPACE" (20).
C141 JR Z,SkipDelimiters_Loop2
C143 CP $2C Jump to SkipDelimiters_Loop2 if the character is an ASCII comma (2C).
C145 JR Z,SkipDelimiters_Loop2
C147 JR ProcessUnrecognisedWords_Loop Jump to ProcessUnrecognisedWords_Loop.
Print the unrecognised word(s) in quotes.
PrintUnrecognisedWord C149 PUSH HL Stash HL on the stack.
Print "I don't know the word:-".
C14A LD HL,$BDA5 HL=Messaging_IDontKnowTheWord.
C14D CALL PrintStringAndNewline Call PrintStringAndNewline.
C150 POP HL Restore HL from the stack.
C151 LD A,$22 Print a double quote character: """.
C153 CALL PrintCharacter
PrintUnrecognisedWord_Loop C156 LD A,(HL) Read the character from *HL and store it in A.
C157 CP $21 Jump to PrintUnrecognisedWord_End if this character is less than 21 (a control character, indicating end of word).
C159 JR C,PrintUnrecognisedWord_End
C15B INC HL Move to the next character in the command buffer.
C15C CALL PrintCharacter Call PrintCharacter.
C15F JR PrintUnrecognisedWord_Loop Jump to PrintUnrecognisedWord_Loop.
PrintUnrecognisedWord_End C161 LD A,$22 Print a double quote character: """.
C163 CALL PrintCharacter
Print ".".
C166 LD HL,$BF29 HL=Messaging_FullStop.
C169 CALL PrintStringAndNewline Call PrintStringAndNewline.
C16C JR ReturnToInputHandler Jump to ReturnToInputHandler.
Check if the input was empty (no words were tokenised). If tokens were found, return to allow the command to be processed. Otherwise, display "I Don't Understand".
CheckIfEmptyInput C16E LD A,($BD66) Return if *UserInput_FirstToken is not equal to FF (input was not empty).
C171 CP $FF
C173 RET NZ
Print "I don't understand.".
C174 LD HL,$BD91 HL=Messaging_IDontUnderstand.
C177 CALL PrintStringAndNewline Call PrintStringAndNewline.
ReturnToInputHandler C17A JP Handler_UserInput Jump to Handler_UserInput to wait for the next command input.
View the equivalent code in;
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