Finish implementing embedded sys.f

[rrq/jonasforth.git] / impl.asm

diff --git a/impl.asm b/impl.asm
index a9b8564e19faeb9c6bdf3ed7b8906f1dccf7d533..f6a25cf5b54d420cc016582e6f3d41e0661636a2 100644 (file)
--- a/impl.asm
+++ b/impl.asm
@@ -129,6 +129,60 @@ read_word:
 
   ret
 
+;; Read a word from a buffer. Returns the buffer without the word, as well as
+;; the word that was read (including lengths).
+;;
+;; Inputs:
+;;   * rsi = Input buffer
+;;   * rcx = Length of buffer
+;;
+;; Outputs:
+;;   * rsi = Updated buffer
+;;   * rcx = Length of updated buffer
+;;   * rdi = Word buffer
+;;   * rdx = Length of word buffer
+pop_word:
+.skip_whitespace:
+  mov al, [rsi]
+  cmp al, ' '
+  je .got_whitespace
+  cmp al, $A
+  je .got_whitespace
+  jmp .alpha
+.got_whitespace:
+  ;; The buffer starts with whitespace; discard the first character from the buffer.
+  inc rsi
+  dec rcx
+  jmp .skip_whitespace
+
+.alpha:
+  ;; We got a character that wasn't whitespace. Now read the actual word.
+  mov rdi, rsi ; This is where the word starts
+  mov rdx, 1   ; Length of word
+
+.read_alpha:
+  ;; Extract character from original buffer:
+  inc rsi
+  dec rcx
+
+  ;; When we hit whitespace, we are done with this word
+  mov al, [rsi]
+  cmp al, ' '
+  je .end
+  cmp al, $A
+  je .end
+
+  ;; It wasn't whitespace; add it to word buffer
+  inc rdx
+  jmp .read_alpha
+
+.end:
+  ;; Finally, we want to skip one whitespace character after the word.
+  inc rsi
+  dec rcx
+
+  ret
+
 ;; Parses a string.
 ;;
 ;; Parameters: