From 4170f15b09ccd8bcafc00bb960a6e56670252256 Mon Sep 17 00:00:00 2001
From: Jonas Hvid <mail@johv.dk>
Date: Sat, 3 Oct 2020 20:32:39 +0200
Subject: [PATCH] Implement the 'KEY' primitive for user input

This is a lower-level primitive for getting user input. We now also use this to
implement READ-WORD.
---
 impl.asm | 51 -----------------------------------
 main.asm | 82 +++++++++++++++++++++++++++++++++++++++++++-------------
 2 files changed, 63 insertions(+), 70 deletions(-)

diff --git a/impl.asm b/impl.asm
index ea6c04e..e8cd883 100644
--- a/impl.asm
+++ b/impl.asm
@@ -69,52 +69,6 @@ find:
 .found:
   ret
 
-;; Read a word from standard input. Returns pointer to string containing word as
-;; well as length.
-;;
-;; Results:
-;;   * rdx = Length of string
-;;   * rdi = Pointer to string buffer
-;;
-;; Clobbers pretty much everything.
-read_word:
-.skip_whitespace:
-  ;; Read characters into .char_buffer until one of them is not whitespace.
-  mov rsi, .char_buffer
-  sys_read_char
-
-  ;; We consider newlines and spaces to be whitespace.
-  cmp [.char_buffer], ' '
-  je .skip_whitespace
-  cmp [.char_buffer], $A
-  je .skip_whitespace
-
-.alpha:
-  ;; We got a character that wasn't whitespace. Now read the actual word.
-  mov [.length], 0
-
-.read_alpha:
-  mov al, [.char_buffer]
-  movzx rbx, [.length]
-  mov rsi, .buffer
-  add rsi, rbx
-  mov [rsi], al
-  inc [.length]
-
-  mov rsi, .char_buffer
-  sys_read_char
-
-  cmp [.char_buffer], ' '
-  je .end
-  cmp [.char_buffer], $A
-  jne .read_alpha
-
-.end:
-  mov rdi, .buffer
-  movzx rdx, [.length]
-
-  ret
-
 ;; Read a word from a buffer. Returns the buffer without the word, as well as
 ;; the word that was read (including lengths).
 ;;
@@ -236,11 +190,6 @@ section '.data' readable writable
 find.search_length dq ?
 find.search_buffer dq ?
 
-read_word.max_size = $FF
-read_word.buffer rb read_word.max_size
-read_word.length db ?
-read_word.char_buffer db ?
-
 parse_number.length dq ?
 parse_number.error_msg string "Invalid number: "
 
diff --git a/main.asm b/main.asm
index 4ed478d..537d0e8 100644
--- a/main.asm
+++ b/main.asm
@@ -231,38 +231,77 @@ forth_asm EMIT, 'EMIT'
   popr rsi
   next
 
-;; Read a word and push it onto the stack as a pointer and a size. The pointer
-;; is valid until the next call to READ_WORD.
-forth_asm READ_WORD, 'READ-WORD'
+;; Read a single character from the current input stream. Usually, this will wait
+;; for the user to press a key, and then return the corresponding character. When
+;; reading from a special buffer, it will instead return the next characater from
+;; that buffer.
+;;
+;; The ASCII character code is placed on the stack.
+forth_asm KEY, 'KEY'
+  call .impl
+  push rax
+  next
+
+;; Result in RAX
+.impl:
   ;; Are we reading from user input or from the input buffer?
   cmp [input_buffer], 0
   jne .from_buffer
 
   ;; Reading user input
-  mov [.rsi], rsi
-
-  call read_word
-  push rdi                      ; Buffer
-  push rdx                      ; Length
+  push rsi
+  mov rsi, .buffer
+  sys_read_char
+  pop rsi
 
-  mov rsi, [.rsi]
-  next
+  movzx rax, byte [.buffer]
+  ret
 
 .from_buffer:
   ;; Reading from buffer
-  mov [.rsi], rsi
+  mov rax, [input_buffer]
+  movzx rax, byte [rax]
 
-  mov rsi, [input_buffer]
-  mov rcx, [input_buffer_length]
+  inc [input_buffer]
+  dec [input_buffer_length]
+  ret
 
-  call pop_word
+;; Read a word and push it onto the stack as a pointer and a size. The pointer
+;; is valid until the next call to READ_WORD.
+forth_asm READ_WORD, 'READ-WORD'
+  push rsi
+.skip_whitespace:
+  ;; Read characters until one of them is not whitespace.
+  call KEY.impl
+  ;; We consider newlines and spaces to be whitespace.
+  cmp al, ' '
+  je .skip_whitespace
+  cmp al, $A
+  je .skip_whitespace
+
+  ;; We got a character that wasn't whitespace. Now read the actual word.
+  mov [.length], 0
 
-  mov [input_buffer], rsi        ; Updated buffer
-  mov [input_buffer_length], rcx ; Length of updated buffer
-  push rdi                       ; Word buffer
-  push rdx                       ; Length of word buffer
+.read_alpha:
+  movzx rbx, [.length]
+  mov rsi, .buffer
+  add rsi, rbx
+  mov [rsi], al
+  inc [.length]
+
+  call KEY.impl
+
+  cmp al, ' '
+  je .end
+  cmp al, $A
+  jne .read_alpha
+
+.end:
+  pop rsi
+  push .buffer
+  movzx rax, [.length]
+  push rax
 
-  mov rsi, [.rsi]
   next
 
 ;; Takes a string on the stack and replaces it with the decimal number that the
@@ -643,6 +682,11 @@ DOTU.rbuffer rq 16
 DOTU.length dq ?
 DOTU.printed_length dq ?
 
+KEY.buffer dq ?
+
+READ_WORD.buffer rb $FF
+READ_WORD.length db ?
+
 ;; Reserve space for compiled words, accessed through HERE.
 here dq here_top
 here_top rq $4000
-- 
2.39.2