From bde84544493bf4ca72fe59eacaecc847a4e54db8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20van=20Dorst?= <opensource@vdorst.com>
Date: Sun, 7 Sep 2025 17:04:46 +0200
Subject: [PATCH] isletter(): optimized version

Less instructions and jumps.
Saves 39 bytes.

```patch
1634,1651c1621,1628
<       mov     r7,a
<       mov     r6,a
< ;     cmd_parser.c:63: return (l >= 'a' && l <= 'z') || (l >= 'A' && l <= 'Z');
<       cjne    r7,#0x61,00326$
< 00326$:
<       mov     _parse_vlan_sloc0_1_0,c
<       jc      00153$
<       mov     a,r7
<       add     a,#0xff - 0x7a
<       mov     _parse_vlan_sloc0_1_0,c
<       jnc     00149$
< 00153$:
<       cjne    r6,#0x41,00329$
< 00329$:
<       mov     _parse_vlan_sloc0_1_0,c
<       jc      00132$
<       mov     a,r6
<       add     a,#0xff - 0x5a
---
> ;     cmd_parser.c:66: l |= 0x20;
> ;     cmd_parser.c:67: l -= 'A';
>       orl     a,#0x20
> ;     cmd_parser.c:68: return (l <= ('Z'-'A'));
>       add     a,#0xbf
>       add     a,#0xff - 0x19
>       cpl     c
> ;     cmd_parser.c:245: if (cmd_words_b[2] > 0 && isletter(cmd_buffer[cmd_words_b[2]])) {
1653,1654c1630
<       jc      00132$
< 00149$:
---
>       jnc     00132$
```
---
 cmd_parser.c      | 7 ++++++-
 rtlplayground.mem | 2 +-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/cmd_parser.c b/cmd_parser.c
index 27eb596..bf09cdf 100644
--- a/cmd_parser.c
+++ b/cmd_parser.c
@@ -60,7 +60,12 @@ __code uint8_t phys_to_log_port[6] = {
 
 inline uint8_t isletter(uint8_t l)
 {
-	return (l >= 'a' && l <= 'z') || (l >= 'A' && l <= 'Z');
+	// return (l >= 'a' && l <= 'z') || (l >= 'A' && l <= 'Z');
+
+	// Make it upper case
+	l |= 0x20;
+	l -= 'A';
+	return (l <= ('Z'-'A'));
 }
 
 
diff --git a/rtlplayground.mem b/rtlplayground.mem
index 7626c2d..cc92f39 100644
--- a/rtlplayground.mem
+++ b/rtlplayground.mem
@@ -26,4 +26,4 @@ Other memory:
    ---------------- -------- -------- -------- --------
    PAGED EXT. RAM                         0      256   
    EXTERNAL RAM     0x0001   0x1ae8    6888    16777216
-   ROM/EPROM/FLASH  0x0000   0x1c71b  47003    16777216
+   ROM/EPROM/FLASH  0x0000   0x1c6f2  46962    16777216