[PATCH] dc: Support base 2 output

[Nate Case]

Add support for base 2 as an output base in dc, so that you can
do things like 'echo "1234 2 o p" | dc' to convert to binary.

Signed-off-by: Nate Case <ncase at xes-inc.com>
---
 miscutils/Config.in |    7 +++++++
 miscutils/dc.c      |   31 +++++++++++++++++++++++++++++--
 2 files changed, 36 insertions(+), 2 deletions(-)

'make bloatcheck' with CONFIG_ENABLE_FEATURE_DC_BASE2=n, where
baseline is unpatched:

function                                             old     new   delta
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/0 up/down: 0/0)                 Total: 0 bytes
   text    data     bss     dec     hex filename
 382228    1898    8916  393042   5ff52 busybox_old
 382228    1898    8916  393042   5ff52 busybox_unstripped

'make bloatcheck' with CONFIG_ENABLE_FEATURE_DC_BASE2=y, where
baseline is unpatched:

function                                             old     new   delta
print_base                                            87     222    +135
set_output_base                                       81      86      +5
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 140/0)             Total: 140 bytes
   text    data     bss     dec     hex filename
 382228    1898    8916  393042   5ff52 busybox_old
 382368    1898    8916  393182   5ffde busybox_unstripped

Index: miscutils/dc.c
===================================================================
--- miscutils/dc.c	(revision 23861)
+++ miscutils/dc.c	(working copy)
@@ -99,7 +99,11 @@
 static void set_output_base(void)
 {
 	base = (unsigned)pop();
+#if ENABLE_FEATURE_DC_BASE2
+	if ((base != 10) && (base != 16) && (base != 2)) {
+#else
 	if ((base != 10) && (base != 16)) {
+#endif
 		bb_error_msg("error, base %d is not supported", base);
 		base = 10;
 	}
@@ -107,10 +111,33 @@
 
 static void print_base(double print)
 {
-	if (base == 16)
+	switch (base) {
+	case 16:
 		printf("%x\n", (unsigned)print);
-	else
+		break;
+#if ENABLE_FEATURE_DC_BASE2
+	case 2:
+		{
+			int i, foundone=0;
+			unsigned x = (unsigned)print;
+			for (i = sizeof(unsigned) * 8 - 1; i >= 0; i--) {
+				if (x & (1 << i)) {
+					foundone = 1;
+					printf("1");
+				} else {
+					if (foundone)
+						printf("0");
+				}
+			}
+			if (!foundone)
+				printf("0");
+			printf("\n");
+		}
+		break;
+#endif
+	default:
 		printf("%g\n", print);
+	}
 }
 
 static void print_stack_no_pop(void)
Index: miscutils/Config.in
===================================================================
--- miscutils/Config.in	(revision 23861)
+++ miscutils/Config.in	(working copy)
@@ -146,6 +146,13 @@
 	  Enable power and exp functions.
 	  NOTE: This will require libm to be present for linking.
 
+config FEATURE_DC_BASE2
+	bool "Enable base 2 support"
+	default n
+	depends on DC
+	help
+	  Enable binary (base 2) as an output base in dc.
+
 config DEVFSD
 	bool "devfsd (obsolete)"
 	default n