libc/picolibc: Support 'minimal' printf mode

Picolibc's 'minimal' printf mode reduces functionality and size even more
than the 'integer' mode. Use this where memory is at a premium and where
the application knows that it does not require exact printf semantics.

Signed-off-by: Keith Packard <keithp@keithp.com>

lib/libc/picolibc/CMakeLists.txt

@@ -17,6 +17,9 @@ if(NOT CONFIG_PICOLIBC_USE_MODULE)
   if(CONFIG_PICOLIBC_IO_FLOAT)
     zephyr_compile_definitions(PICOLIBC_DOUBLE_PRINTF_SCANF)
     zephyr_link_libraries(-DPICOLIBC_DOUBLE_PRINTF_SCANF)
+  elseif(CONFIG_PICOLIBC_IO_MINIMAL)
+    zephyr_compile_definitions(PICOLIBC_MINIMAL_PRINTF_SCANF)
+    zephyr_link_libraries(-DPICOLIBC_MINIMAL_PRINTF_SCANF)
   else()
     zephyr_compile_definitions(PICOLIBC_INTEGER_PRINTF_SCANF)
     zephyr_link_libraries(-DPICOLIBC_INTEGER_PRINTF_SCANF)

lib/libc/picolibc/Kconfig

@@ -28,13 +28,38 @@ config PICOLIBC_HEAP_SIZE
 config PICOLIBC_IO_LONG_LONG
 	bool "support for long long in integer-only printf/scanf"
 	help
-	  Includes support for long long in integer-only printf/scanf. long long
-	  types are always supported in the floating-point versions.
+	  Includes support for long long in minimal printf/scanf. long
+	  long types are always supported in the integer and
+	  floating-point versions.
+
+choice PICOLIBC_IO_LEVEL
+	prompt "Picolibc printf/scanf level"
+	default PICOLIBC_IO_MINIMAL if CBPRINTF_NANO
+	default PICOLIBC_IO_INTEGER
+	help
+	  Selects the level of printf and scanf support
 
 config PICOLIBC_IO_FLOAT
-	bool "support for floating point values in printf/scanf"
+	bool "full support for integer/floating point values in printf/scanf"
+	help
+	  Include full floating point and integer support in printf/scanf
+	  functions.
+
+config PICOLIBC_IO_INTEGER
+	bool "full support for integer values in printf/scanf"
+	depends on !CBPRINTF_FP_SUPPORT
+	help
+	  Include full integer, but no floating point support in
+	  printf/scanf.
+
+config PICOLIBC_IO_MINIMAL
+	bool "limited support for integer values in printf/scanf"
+	depends on !CBPRINTF_FP_SUPPORT
 	help
-	  Include floating point support in printf/scanf functions.
+	  Include limited integer and no floating point suppor tin
+	  printf/scanf.
+
+endchoice
 
 if PICOLIBC_USE_MODULE
 
@@ -94,14 +119,15 @@ config PICOLIBC_ASSERT_VERBOSE
 config PICOLIBC_IO_C99_FORMATS
 	bool "support C99 format additions in printf/scanf"
 	default y
+	depends on !PICOLIBC_IO_MINIMAL
 	help
 	  Includes support for hex floats (in floating-point version) and j, z,
 	  t size modifiers.
 
 config PICOLIBC_IO_POS_ARGS
 	bool "Support POSIX positional args (e.g. %$1d) in printf/scanf"
 	default y
-	depends on !PICOLIBC_IO_FLOAT
+	depends on PICOLIBC_IO_INTEGER
 	help
 	  Includes support for positional args (e.g. $1) in integer-only printf
 	  and scanf. Positional args are always supported in the floating-point
@@ -115,6 +141,14 @@ config PICOLIBC_IO_FLOAT_EXACT
 	  This ensures that printf values with enough digits can be
 	  fed to scanf and generate exactly the same binary value.
 
+config PICOLIBC_IO_SMALL_ULTOA
+	bool "avoid soft division in printf"
+	default y if PICOLIBC_IO_MINIMAL || PICOLIBC_IO_INTEGER && PICOLIBC_IO_LONG_LONG
+	help
+	  Replaces division and modulus by 10 with shifts and adds when
+	  doing binary to decimal conversion in printf for targets with
+	  no hardware divider.
+
 config PICOLIBC_LOCALE_INFO
 	bool "support locales in libc functions"
 	help

lib/os/Kconfig.cbprintf

@@ -67,7 +67,6 @@ config CBPRINTF_FP_SUPPORT
 	bool "Floating point formatting in cbprintf"
 	default y if FPU
 	depends on CBPRINTF_COMPLETE
-	select PICOLIBC_IO_FLOAT if PICOLIBC
 	help
 	  Build the cbprintf utility function with support for floating
 	  point format specifiers.  Selecting this increases stack size