forth-riscv

commit f903c057c9c6fc6b5d21281b82043aa9e04b08be
parent 2d633a55cc7463e140c4bd2b10475c947386d6cc
Author: Christian Ermann <christian.ermann@joescan.com>
Date:   Fri, 11 Jul 2025 19:32:48 -0700

Fix 'literal' for immediates with bit 12 set

Diffstat:
M
src/forth.s
 | 
29
+++++++++++++++++++----------

1 file changed, 19 insertions(+), 10 deletions(-)
diff --git a/src/forth.s b/src/forth.s
@@ -698,41 +698,50 @@ _postpone_fail:
 _postpone_done:
     exit
 
-defword "literal", literal, 0xECB9D8E4, flags=flag_immediate
-    push w
-    li w, 0xFFC10113 # addi psp, psp, -4
+defword "push,", push_comma, 0x264FE863, flags=flag_immediate
     push w
     li w, 0xFEA12E23 # sw w, -4(psp)
     jal lit_comma
+    push w
+    li w, 0xFFC10113 # addi psp, psp, -4
     jal lit_comma
+    exit
+
+defword "literal", literal, 0xECB9D8E4, flags=flag_immediate
+    jal push_comma
     mv x, w
 _literal_small_1:
-    # emit `addi w, zero, immed`
+    # encode `addi w, zero, immed`
     andi w, x, -1 # 0xFFF
     slli w, w, 20
     addi w, w, 0x513
+    # when immed > 4095, we need to use a 2 instruction sequence
     li y, 0xFFF
-    bltu x, y, _literal_small_2
+    bgtu x, y, _literal_large_1
+    # when bit 12 isn't set, we're done
+    srli y, x, 11
+    andi y, y, 1
+    beqz y, _literal_small_2
 _literal_large_1:
-    # change to `addi w, w, immed`
+    # change `addi w, zero, immed` to `addi w, w, immed`
     li y, 0xA
     slli y, y, 15
     add w, w, y
     push w
-    # encode upper immediate
+    # encode `lui w, immed`
     li w, 0xFFFFF000
     and w, x, w
+    # when bit 12 is set, we need to correct for sign ext. from 'addi'
     srli y, x, 11
     andi y, y, 1
     beqz y, _literal_large_2
     li y, 0x00001000
     add w, w, y
 _literal_large_2:
-    # emit `lui w, immed`
     addi w, w, 0x537
-    jal lit_comma
+    jal lit_comma # emits `lui`
 _literal_small_2:
-    jal lit_comma
+    jal lit_comma # emits `addi`
     exit
 
 defcode "word>hash", word_to_hash, 0x50E0A245