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Compiling...
/usr/local/CodeSourcery/bin/arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb --no-builtin-memcpy --no-builtin-memset -std=gnu99 -O1 -g -c ./source/startup.c ./source/system_LPC17xx.c ./source/main.c ./source/misc.c ./source/leds.c ./source/timer.c ./source/uart.c ./source/pwm.c ./source/gps.c ./source/i2c.c ./source/itg3200.c ./source/bma180.c
Done!
Linking...
/usr/local/CodeSourcery/bin/arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb --no-builtin-memcpy --no-builtin-memset -T link.T -Wl,--build-id=none startup.o system_LPC17xx.o main.o misc.o leds.o timer.o uart.o pwm.o gps.o i2c.o itg3200.o bma180.o -o main.elf
main.o: In function `main':
/media/FCB7-6FF5/Quadrocopter/Koder/Quad_code/./source/main.c:33: undefined reference to `sqrtf'
collect2: ld returned 1 exit status
make: *** [main.elf] Error 1

CC = /usr/local/CodeSourcery/bin/arm-none-eabi-gcc
COMMON = -mcpu=cortex-m3 -mthumb --no-builtin-memcpy --no-builtin-memset
CFLAGS = $(COMMON) -std=gnu99 -O1 -g
LDFLAGS = $(COMMON) -T link.T -Wl,--build-id=none
DIR = ./source/
SRCC = $(DIR)startup.c $(DIR)system_LPC17xx.c $(DIR)main.c $(DIR)misc.c $(DIR)leds.c
SRCC += $(DIR)timer.c $(DIR)uart.c $(DIR)pwm.c $(DIR)gps.c $(DIR)i2c.c $(DIR)itg3200.c
SRCC += $(DIR)bma180.c
SRCO = startup.o system_LPC17xx.o main.o misc.o leds.o timer.o uart.o pwm.o gps.o i2c.o
SRCO += itg3200.o bma180.o

all: clean main.elf

main.o: $(SRC)
@echo "Compiling..."
$(CC) $(CFLAGS) -c $(SRCC)
@echo "Done!"

main.elf: main.o
@echo "Linking..."
$(CC) $(LDFLAGS) $(SRCO) -o main.elf
@echo "Done!"

clean:
@echo "Cleaning..."
rm -f *.o *.elf

This chapter documents the mathematical functions provided by CSLIBC.
In addition to including math.h in your source code, you must link with
the math library (-lm) to use the functions listed in this chapter.

I've been reading that by default there is an -mthumb compiler flag which reduces code size by 35%.
However, in a floating-point calculation intensive app like mine, this is not an good option, like apple says.
I'd like to try it out if it changes anything.