[U-Boot] [PATCH 7/7] cmd_setexpr: allow memory addresses and env vars in expressions

[Frans Meulenbroeks]

This patch add functionality to use memory addresses and environment variables in
expressions. This increases the power of expressions substantially

It adheres to the standard convemtions: memory addresses can be given in the format
*address (e.g. *1000), environment variables as $this_var.
environment variables are not processed recursively but can contain both constants
and memory addresses.

Rationale for this change is that it allows masking off bits from a byte that is
obtained by reading data from e.g. i2c.

Signed-off-by: Frans Meulenbroeks <fransmeulenbroeks at gmail.com>

---

If recursive environment vars is desired: this can be added easily by changing the
if statement into a while statement.
I figured that would be somewhat over the top though (and, unless you take
special precautions you can run into an endless loop if an env var contains
its own name.
If it is desired, please let me know and I happily will add it.

And a snippet from the test log:
=> mm.b 1000
00001000: de ? 12
00001001: ad ? 34
00001002: be ? 56
00001003: ef ? 78
00001004: de ?
00001005: ad ? .
=> setexpr aap 3 + *1000
=> echo $aap
1234567b
=> setexpr.b aap 3 + *1000
=> echo $aap
15
=> setexpr.w nut $aap + *1000
=> echo $nut
1249
---
 common/cmd_setexpr.c |   33 +++++++++++++++++++++++++++++----
 1 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/common/cmd_setexpr.c b/common/cmd_setexpr.c
index f8b5d4d..6ea9296 100644
--- a/common/cmd_setexpr.c
+++ b/common/cmd_setexpr.c
@@ -28,10 +28,32 @@
 #include <config.h>
 #include <command.h>
 
+static ulong get_arg(char *s, int w)
+{
+	ulong *p;
+
+	/* if the parameter starts with a $ replace it with the environment value */
+	if (s[0] == '$') {
+		s = getenv(&s[1]);
+	}
+	/* if the parameter starts with a * then assume is a pointer to the value we want */
+	if (s[0] == '*') {
+		p = (ulong *)simple_strtoul(&s[1], NULL, 16);
+		switch (w) {
+		case 1: return((ulong)(*(uchar *)p));
+		case 2: return((ulong)(*(ushort *)p));
+		case 4: return(*p);
+		}
+	} else {
+		return simple_strtoul(s, NULL, 16);
+	}
+}
+
 int do_setexpr(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 {
 	ulong a, b;
 	char buf[16];
+	int w;
 
 	/* Validate arguments */
 	if ((argc != 5) || (strlen(argv[3]) != 1)) {
@@ -39,8 +61,10 @@ int do_setexpr(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 		return 1;
 	}
 
-	a = simple_strtoul(argv[2], NULL, 16);
-	b = simple_strtoul(argv[4], NULL, 16);
+	w = cmd_get_data_size(argv[0], 4);
+
+	a = get_arg(argv[2], w);
+	b = get_arg(argv[4], w);
 
 	switch (argv[3][0]) {
 	case '|': sprintf(buf, "%lx", (a | b)); break;
@@ -64,7 +88,8 @@ int do_setexpr(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 U_BOOT_CMD(
 	setexpr, 5, 0, do_setexpr,
 	"set environment variable as the result of eval expression",
-	"name value1 <op> value2\n"
+	"[.b, .w, .l] name value1 <op> value2\n"
 	"    - set environment variable 'name' to the result of the evaluated\n"
-	"      express specified by <op>.  <op> can be &, |, ^, +, -, *, /, %"
+	"      express specified by <op>.  <op> can be &, |, ^, +, -, *, /, %\n"
+	"      size argument is only meaningful if value1 and/or value2 are memory addresses"
 );
-- 
1.7.0