1. Use lib/libm for small (non-Express builds) to gain back a lot of flash space.

2. Add flag INTERNAL_LIBM to mpconfigboard.mk files to signal using lib/libm.
3. Fix floating-point warnings in lib/libm
4. Turn off -finline-limit, no longer needed due to 1.
5. Add explicit flags for SPI_FLASH_FILESYSTEM and INTERNAL_FLASH_FILESYSTEM
to mpconfigboard.mk files, so they don't need to know the name of the .c file
that implements those. Makefile takes care of checking the flags and including
the right files.

atmel-samd/Makefile

@@ -135,11 +135,12 @@ ifeq ($(DEBUG), 1)
 # -DMICROPY_DEBUG_MODULES may also be added to an -flto build, if you wish.
 CFLAGS += -Os -ggdb -DNDEBUG -DENABLE_MICRO_TRACE_BUFFER -DMICROPY_DEBUG_MODULES
 else
-# GCC_INLINE_LIMIT specifies -finline-limit, which can shrink the image size.
+# -finline-limit can shrink the image size.
 # -finline-limit=80 or so is similar to not having it on.
 # There is no simple default value, though.
-ifeq ($(FLASH_IMPL),internal_flash.c)
-GCC_INLINE_LIMIT = -finline-limit=19
+ifdef INTERNAL_FLASH_FILESYSTEM
+  ## Not currently needed
+  ## CFLAGS += -finline-limit=50
 endif
 CFLAGS += -Os -DNDEBUG -flto $(GCC_INLINE_LIMIT)
 endif
@@ -161,10 +162,14 @@ CFLAGS += -DMICROPY_MODULE_FROZEN_MPY
 CFLAGS += -Wno-error=lto-type-mismatch
 endif
 
-#LIBM_FILE_NAME   = $(shell $(CC) $(CFLAGS) -print-file-name=libm.a)
 LDFLAGS = $(CFLAGS) -nostartfiles -fshort-enums -mthumb -mcpu=cortex-m0plus -Lasf/thirdparty/CMSIS/Lib/GCC/ -Wl,-nostdlib -Wl,-T,$(LD_FILE) -Wl,-Map=$@.map -Wl,-cref -Wl,-gc-sections -specs=nano.specs
 LIBS = -larm_cortexM0l_math -lm -lgcc -lc
 
+# Use toolchain libm if we're not using our own.
+ifndef INTERNAL_LIBM
+LIBS += -lm
+endif
+
 SRC_ASF = $(addprefix asf/sam0/,\
 	drivers/adc/adc_sam_d_r/adc.c \
 	drivers/dac/dac_sam_d_c/dac.c \
@@ -237,6 +242,16 @@ SRC_C = \
 	lib/libc/string0.c \
 	lib/mp-readline/readline.c
 
+# Choose which flash filesystem impl to use.
+# (Right now INTERNAL_FLASH_FILESYSTEM and SPI_FLASH_FILESYSTEM are mutually exclusive.
+# But that might not be true in the future.)
+ifdef INTERNAL_FLASH_FILESYSTEM
+SRC_C += internal_flash.c
+endif
+ifdef SPI_FLASH_FILESYSTEM
+SRC_C += spi_flash.c
+endif
+
 SRC_COMMON_HAL = \
 	analogio/__init__.c \
 	analogio/AnalogIn.c \
@@ -270,6 +285,30 @@ SRC_COMMON_HAL = \
 	usb_hid/__init__.c \
 	usb_hid/Device.c
 
+ifdef INTERNAL_LIBM
+SRC_LIBM = $(addprefix lib/,\
+	libm/math.c \
+	libm/fmodf.c \
+	libm/nearbyintf.c \
+	libm/ef_sqrt.c \
+	libm/kf_rem_pio2.c \
+	libm/kf_sin.c \
+	libm/kf_cos.c \
+	libm/kf_tan.c \
+	libm/ef_rem_pio2.c \
+	libm/sf_sin.c \
+	libm/sf_cos.c \
+	libm/sf_tan.c \
+	libm/sf_frexp.c \
+	libm/sf_modf.c \
+	libm/sf_ldexp.c \
+	libm/asinfacosf.c \
+	libm/atanf.c \
+	libm/atan2f.c \
+	)
+endif
+
+
 # These don't have corresponding files in each port but are still located in
 # shared-bindings to make it clear what the contents of the modules are.
 SRC_BINDINGS_ENUMS = \
@@ -304,6 +343,9 @@ OBJ = $(PY_O) $(addprefix $(BUILD)/, $(SRC_C:.c=.o))
 OBJ += $(addprefix $(BUILD)/, $(SRC_ASF:.c=.o))
 OBJ += $(addprefix $(BUILD)/, $(SRC_COMMON_HAL_EXPANDED:.c=.o))
 OBJ += $(addprefix $(BUILD)/, $(SRC_SHARED_MODULE_EXPANDED:.c=.o))
+ifdef INTERNAL_LIBM
+OBJ += $(addprefix $(BUILD)/, $(SRC_LIBM:.c=.o))
+endif
 
 SRC_QSTR += $(SRC_C) $(SRC_COMMON_HAL_EXPANDED) $(SRC_SHARED_MODULE_EXPANDED) $(STM_SRC_C)
 

atmel-samd/boards/arduino_zero/mpconfigboard.mk

@@ -2,6 +2,7 @@ LD_FILE = boards/samd21x18-bootloader.ld
 USB_VID = 0x2341
 USB_PID = 0x824D
 
-FLASH_IMPL = internal_flash.c
+INTERNAL_FLASH_FILESYSTEM = 1
+INTERNAL_LIBM = 1
 
 CHIP_VARIANT = SAMD21G18A

atmel-samd/boards/circuitplayground_express/mpconfigboard.mk

@@ -2,7 +2,7 @@ LD_FILE = boards/samd21x18-bootloader-external-flash-crystalless.ld
 USB_VID = 0x239A
 USB_PID = 0x8019
 
-FLASH_IMPL = spi_flash.c
+SPI_FLASH_FILESYSTEM = 1
 
 CHIP_VARIANT = SAMD21G18A
 

atmel-samd/boards/feather_m0_adalogger/mpconfigboard.mk

@@ -2,6 +2,7 @@ LD_FILE = boards/samd21x18-bootloader.ld
 USB_VID = 0x239A
 USB_PID = 0x8015
 
-FLASH_IMPL = internal_flash.c
+INTERNAL_FLASH_FILESYSTEM = 1
+INTERNAL_LIBM = 1
 
 CHIP_VARIANT = SAMD21G18A

atmel-samd/boards/feather_m0_basic/mpconfigboard.mk

@@ -2,7 +2,8 @@ LD_FILE = boards/samd21x18-bootloader.ld
 USB_VID = 0x239A
 USB_PID = 0x8015
 
-FLASH_IMPL = internal_flash.c
+INTERNAL_FLASH_FILESYSTEM = 1
+INTERNAL_LIBM = 1
 
 CHIP_VARIANT = SAMD21G18A
 

atmel-samd/boards/feather_m0_express/mpconfigboard.mk

@@ -2,6 +2,6 @@ LD_FILE = boards/samd21x18-bootloader-external-flash.ld
 USB_VID = 0x239A
 USB_PID = 0x801b
 
-FLASH_IMPL = spi_flash.c
+SPI_FLASH_FILESYTEM = 1
 
 CHIP_VARIANT = SAMD21G18A

atmel-samd/boards/gemma_m0/mpconfigboard.mk

@@ -2,6 +2,7 @@ LD_FILE = boards/samd21x18-bootloader.ld
 USB_VID = 0x239A
 USB_PID = 0x801D
 
-FLASH_IMPL = internal_flash.c
+INTERNAL_FLASH_FILESYSTEM = 1
+INTERNAL_LIBM = 1
 
 CHIP_VARIANT = SAMD21E18A

atmel-samd/boards/metro_m0_express/mpconfigboard.mk

@@ -2,6 +2,6 @@ LD_FILE = boards/samd21x18-bootloader-external-flash.ld
 USB_VID = 0x239A
 USB_PID = 0x8014
 
-FLASH_IMPL = spi_flash.c
+SPI_FLASH_FILESYSTEM = 1
 
 CHIP_VARIANT = SAMD21G18A

atmel-samd/boards/trinket_m0/mpconfigboard.mk

@@ -2,6 +2,7 @@ LD_FILE = boards/samd21x18-bootloader.ld
 USB_VID = 0x239A
 USB_PID = 0x801F
 
-FLASH_IMPL = internal_flash.c
+INTERNAL_FLASH_FILESYSTEM = 1
+INTERNAL_LIBM = 1
 
 CHIP_VARIANT = SAMD21E18A

atmel-samd/boards/trinket_m0_haxpress/mpconfigboard.mk

@@ -2,7 +2,7 @@ LD_FILE = boards/samd21x18-bootloader-external-flash-crystalless.ld
 USB_VID = 0x239A
 USB_PID = 0x801F
 
-FLASH_IMPL = spi_flash.c
+SPI_FLASH_FILESYSTEM = 1
 
 CHIP_VARIANT = SAMD21E18A
 CHIP_FAMILY = samd21

atmel-samd/mpconfigport.h

@@ -189,6 +189,8 @@ extern const struct _mp_obj_module_t usb_hid_module;
     #define MICROPY_PY_FRAMEBUF         (0)
     #define EXTRA_BUILTIN_MODULES
 
+    #define MICROPY_PY_BUILTINS_COMPLEX (0)
+
     #define MICROPY_BUILTIN_METHOD_CHECK_SELF_ARG (0)
     #define MICROPY_CPYTHON_COMPAT      (0)
 #endif

lib/libm/ef_rem_pio2.c

@@ -151,7 +151,7 @@ pio2_3t =  6.1232342629e-17; /* 0x248d3132 */
 	    fn = (float)n;
 	    r  = t-fn*pio2_1;
 	    w  = fn*pio2_1t;	/* 1st round good to 40 bit */
-	    if(n<32&&(ix&0xffffff00)!=npio2_hw[n-1]) {	
+	    if(n<32&&(__int32_t)(ix&0xffffff00)!=npio2_hw[n-1]) {	
 		y[0] = r-w;	/* quick check no cancellation */
 	    } else {
 	        __uint32_t high;
@@ -195,7 +195,10 @@ pio2_3t =  6.1232342629e-17; /* 0x248d3132 */
 	}
 	tx[2] = z;
 	nx = 3;
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wfloat-equal"
 	while(tx[nx-1]==zero) nx--;	/* skip zero term */
+#pragma GCC diagnostic pop
 	n  =  __kernel_rem_pio2f(tx,y,e0,nx,2,two_over_pi);
 	if(hx<0) {y[0] = -y[0]; y[1] = -y[1]; return -n;}
 	return n;

lib/libm/kf_rem_pio2.c

@@ -138,7 +138,10 @@ recompute:
 	}
 
     /* check if recomputation is needed */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wfloat-equal"
 	if(z==zero) {
+#pragma GCC diagnostic pop           
 	    j = 0;
 	    for (i=jz-1;i>=jk;i--) j |= iq[i];
 	    if(j==0) { /* need recomputation */
@@ -155,7 +158,10 @@ recompute:
 	}
 
     /* chop off zero terms */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wfloat-equal"
 	if(z==(float)0.0) {
+#pragma GCC diagnostic pop
 	    jz -= 1; q0 -= 8;
 	    while(iq[jz]==0) { jz--; q0-=8;}
 	} else { /* break z into 8-bit if necessary */

lib/libm/math.c

@@ -338,7 +338,7 @@ float powf(float x, float y)
 			return sn*huge*huge;  /* overflow */
 	} else if ((j&0x7fffffff) > 0x43160000)  /* z < -150 */ // FIXME: check should be  (uint32_t)j > 0xc3160000
 		return sn*tiny*tiny;  /* underflow */
-	else if (j == 0xc3160000) {  /* z == -150 */
+	else if (j == (int32_t) 0xc3160000) {  /* z == -150 */
 		if (p_l <= z-p_h)
 			return sn*tiny*tiny;  /* underflow */
 	}
@@ -585,13 +585,13 @@ float expm1f(float x)
 /*****************************************************************************/
 /*****************************************************************************/
 
-/* k is such that k*ln2 has minimal relative error and x - kln2 > log(FLT_MIN) */
-static const int k = 235;
-static const float kln2 = 0x1.45c778p+7f;
 
 /* expf(x)/2 for x >= log(FLT_MAX), slightly better than 0.5f*expf(x/2)*expf(x/2) */
 float __expo2f(float x)
 {
+	/* k is such that k*ln2 has minimal relative error and x - kln2 > log(FLT_MIN) */
+	static const int k = 235;
+	static const float kln2 = 0x1.45c778p+7f;
 	float scale;
 
 	/* note that k is odd and scale*scale overflows */

lib/libm/nearbyintf.c

@@ -15,7 +15,10 @@ float nearbyintf(float x)
 		y = x - 0x1p23f + 0x1p23f;
 	else
 		y = x + 0x1p23f - 0x1p23f;
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wfloat-equal"
 	if (y == 0)
+#pragma GCC diagnostic pop
 		return s ? -0.0f : 0.0f;
 	return y;
 }

lib/libm/sf_ldexp.c

@@ -32,7 +32,10 @@
 	float value; int exp;
 #endif
 {
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wfloat-equal"
 	if(!isfinite(value)||value==(float)0.0) return value;
+#pragma GCC diagnostic pop
 	value = scalbnf(value,exp);
 	//if(!finitef(value)||value==(float)0.0) errno = ERANGE;
 	return value;