[U-Boot-Users] [RFC/PATCH] Add expr command

[U-Boot-Users] [RFC/PATCH] Add expr command

[Kumar Gala]

Add a simple expr command that will set an env variable as the result
of the command.  This allows us to do simple math in shell.  The following
operations are supported: &, |, +, -, *, /.

---

I'd like to add this to the default command set in include/config_cmd_default.h
but wanted to get feedback on the command before doing that.

 common/Makefile   |    1 +
 common/cmd_expr.c |   69 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 70 insertions(+), 0 deletions(-)
 create mode 100644 common/cmd_expr.c

diff --git a/common/Makefile b/common/Makefile
index 1639109..4f3e711 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -54,6 +54,7 @@ COBJS-$(CONFIG_CMD_DOC) += cmd_doc.o
 COBJS-$(CONFIG_CMD_DTT) += cmd_dtt.o
 COBJS-y += cmd_eeprom.o
 COBJS-$(CONFIG_CMD_ELF) += cmd_elf.o
+COBJS-$(CONFIG_CMD_EXPR) += cmd_expr.o
 COBJS-$(CONFIG_CMD_EXT2) += cmd_ext2.o
 COBJS-$(CONFIG_CMD_FAT) += cmd_fat.o
 COBJS-y += cmd_fdc.o
diff --git a/common/cmd_expr.c b/common/cmd_expr.c
new file mode 100644
index 0000000..d9233df
--- /dev/null
+++ b/common/cmd_expr.c
@@ -0,0 +1,69 @@
+/*
+ * Copyright 2008 Freescale Semiconductor, Inc.
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+/*
+ * This file provides a shell like 'expr' function to return.
+ */
+
+#include <common.h>
+#include <config.h>
+#include <command.h>
+
+int do_expr (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+{
+	ulong a, b;
+	char buf[16];
+
+	/* Validate arguments */
+	if ((argc != 5)) {
+		printf("Usage:\n%s\n", cmdtp->usage);
+		return 1;
+	}
+
+	a = simple_strtoul(argv[2], NULL, 16);
+	b = simple_strtoul(argv[4], NULL, 16);
+
+	switch (argv[3][0]) {
+	case '|': sprintf(buf, "%lx", (a | b)); break;
+	case '&': sprintf(buf, "%lx", (a & b)); break;
+	case '+': sprintf(buf, "%lx", (a + b)); break;
+	case '-': sprintf(buf, "%lx", (a - b)); break;
+	case '*': sprintf(buf, "%lx", (a * b)); break;
+	case '/': sprintf(buf, "%lx", (a / b)); break;
+	case '%': sprintf(buf, "%lx", (a % b)); break;
+	default:
+		printf("invalid op\n");
+		return 1;
+	}
+
+	setenv(argv[1], buf);
+
+	return 0;
+}
+
+U_BOOT_CMD(
+	expr, 5, 0, do_expr,
+	"expr    - set environment variable as the result of eval expression\n",
+	"name value1 <op> value2\n"
+	"    - set environment variable 'name' to the result of the evaluated\n"
+	"      express specified by <op>.  <op> can be &, |, +, -, *, /, %\n"
+);
-- 
1.5.3.8

[U-Boot-Users] [RFC/PATCH] Add expr command

[Andreas Schweigstill]

Hello!

Kumar Gala schrieb:
> Add a simple expr command that will set an env variable as the result
> of the command.

Good idea! I have been missing this for a long time but I also was too
lazy to implement it.

> +	/* Validate arguments */
> +	if ((argc != 5)) {
> +		printf("Usage:\n%s\n", cmdtp->usage);
> +		return 1;
> +	}

It should also be checked if the operator has a length of exactly
one character in order to prevent typos.

+	/* Validate arguments */
+	if ((argc != 5) || (strlen(argv[3]) != 1)) {
+		printf("Usage:\n%s\n", cmdtp->usage);
+		return 1;
+	}

May we rely on the compiler optimizing the above expression so
strlen() != 1 will only be evaluated if argc == 5 ? Probably we
have to write

+	ulong a, b;
+	char buf[16];
+	int valid = 0;
+
+	/* Validate arguments */
+	if (argc == 5) {
+		if (strlen(argv[3]) == 1) {
+			valid = 1;
+		}
+	}
+	if (!valid) {
+		printf("Usage:\n%s\n", cmdtp->usage);
+		return 1;
+	}

Regards
Andreas Schweigstill


-- 
Dipl.-Phys. Andreas Schweigstill
Schweigstill IT | Embedded Systems
Schauenburgerstra?e 116, D-24118 Kiel, Germany
Phone: (+49) 431 5606-435, Fax: (+49) 431 5606-436
Mobile: (+49) 171 6921973, Web: http://www.schweigstill.de/

[U-Boot-Users] [RFC/PATCH] Add expr command

[Scott Wood]

On Wed, Feb 13, 2008 at 03:20:56PM +0100, Andreas Schweigstill wrote:
> +	/* Validate arguments */
> +	if ((argc != 5) || (strlen(argv[3]) != 1)) {
> +		printf("Usage:\n%s\n", cmdtp->usage);
> +		return 1;
> +	}
> 
> May we rely on the compiler optimizing the above expression so
> strlen() != 1 will only be evaluated if argc == 5 ?

Short-circuit evaluation isn't optimization, it's the semantics of the C
language.

-Scott