From ee01f1a7f1e10be78bcceb4f0f42aa352a6a588f Mon Sep 17 00:00:00 2001
From: Jacques Comeaux <jacquesrcomeaux@protonmail.com>
Date: Sat, 24 Aug 2024 01:14:04 -0500
Subject: Add parsers for basic instruction types

---
 newasm/regimm.s | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 newasm/regimm.s

(limited to 'newasm/regimm.s')

diff --git a/newasm/regimm.s b/newasm/regimm.s
new file mode 100644
index 0000000..3e294c8
--- /dev/null
+++ b/newasm/regimm.s
@@ -0,0 +1,37 @@
+.syntax unified
+.cpu cortex-m0plus
+.thumb
+
+.type regimm, %function
+.global regimm
+
+// R1 instruction under construction
+// R3 immediate width
+// R4 input buffer
+
+regimm:   PUSH    {LR}
+          PUSH    {R3}
+          BL      register    // parse a register
+          POP     {R3}
+          BNE     exit        // exit if failure
+          CMP     R2, 7       // check that it's R0-R7
+          BHI     bad_reg
+          LSLS    R2, 8       // shift by 8
+          ORRS    R1, R2      // fill in Rdn
+          BL      whitespace  // mandatory whitespace
+          BNE     exit        // exit if failure
+          PUSH    {R3}
+          BL      immediate
+          POP     {R3}
+          BNE     exit
+          MOVS    R0, 1
+          LSLS    R0, R3
+          CMP     R2, R0
+          BLO     fine
+          MOVS    R0, 0x0A    // returun code 0A (immediate value too large)
+          POP     {PC}
+fine:     ORRS    R1, R2      // fill in imm
+          MOVS    R0, 0       // return code 0 (success)
+exit:     POP     {PC}
+bad_reg:  MOVS    R0, 8       // return code 8 (invalid register for this register position)
+          POP     {PC}
-- 
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