seminaries/qtrvsim: add ffs-as-log2, the fisrt motivation example from lecture.

Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>

seminaries/qtrvsim/ffs-as-log2/.gitignore

+*.o
+depend
+change_me

seminaries/qtrvsim/ffs-as-log2/Makefile

+ARCH=riscv64-unknown-elf
+
+SOURCES = ffs-as-log2.S
+TARGET_EXE = ffs-as-log2
+
+CC=$(ARCH)-gcc
+CXX=$(ARCH)-g++
+AS=$(ARCH)-as
+LD=$(ARCH)-ld
+OBJCOPY=$(ARCH)-objcopy
+
+ARCHFLAGS += -mabi=ilp32
+ARCHFLAGS += -march=rv32i
+ARCHFLAGS += -fno-lto
+
+CFLAGS  += -ggdb -Os -Wall
+CXXFLAGS+= -ggdb -Os -Wall
+AFLAGS  += -ggdb
+LDFLAGS += -ggdb
+LDFLAGS += -nostartfiles
+LDFLAGS += -nostdlib
+LDFLAGS += -static
+#LDFLAGS += -specs=/opt/musl/riscv64-linux-gnu/lib/musl-gcc.specs
+
+CFLAGS  += $(ARCHFLAGS)
+CXXFLAGS+= $(ARCHFLAGS)
+AFLAGS  += $(ARCHFLAGS)
+LDFLAGS += $(ARCHFLAGS)
+
+OBJECTS += $(filter %.o,$(SOURCES:%.S=%.o))
+OBJECTS += $(filter %.o,$(SOURCES:%.c=%.o))
+OBJECTS += $(filter %.o,$(SOURCES:%.cpp=%.o))
+
+all : default
+
+.PHONY : default clean dep all
+
+%.o:%.S
+	$(CC) -D__ASSEMBLY__ $(AFLAGS) -c $< -o $@
+
+%.o:%.c
+	$(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $@
+
+%.o:%.cpp
+	$(CXX) $(CXXFLAGS) $(CPPFLAGS) -c $<
+
+%.s:%.c
+	$(CC) $(CFLAGS) $(CPPFLAGS) -S $< -o $@
+
+default : $(TARGET_EXE)
+
+$(TARGET_EXE) : $(OBJECTS)
+	$(CC) $(LDFLAGS) $^ -o $@
+
+dep: depend
+
+depend: $(SOURCES) $(glob *.h)
+	echo '# autogenerated dependencies' > depend
+ifneq ($(filter %.S,$(SOURCES)),)
+	$(CC)  -D__ASSEMBLY__ $(AFLAGS) -w -E -M $(filter %.S,$(SOURCES)) \
+	  >> depend
+endif
+ifneq ($(filter %.c,$(SOURCES)),)
+	$(CC) $(CFLAGS) $(CPPFLAGS) -w -E -M $(filter %.c,$(SOURCES)) \
+	  >> depend
+endif
+ifneq ($(filter %.cpp,$(SOURCES)),)
+	$(CXX) $(CXXFLAGS) $(CPPFLAGS) -w -E -M $(filter %.cpp,$(SOURCES)) \
+	  >> depend
+endif
+
+clean:
+	rm -f *.o *.a $(OBJECTS) $(TARGET_EXE) depend
+
+#mips-elf-objdump --source -M no-aliases,reg-names=numeric qtmips_binrep
+
+-include depend

seminaries/qtrvsim/ffs-as-log2/ffs-as-log2.S

+// ffs as log2(x)
+.globl _start
+.globl __start
+.option norelax
+.text
+
+__start:
+_start:
+	addi	a0, zero, 157	// int x = 157;
+	addi	t1, zero, -1	// int y = 0;
+	beq	a0, zero, done	// while(x != 0)
+loop:				// {
+	srli	a0, a0, 1		// x = x / 2;
+	addi	t1, t1, 1		// y = y + 1;
+	bne	a0, zero, loop	//}
+done:
+	addi	a0, t1, 0
+finish:	ebreak
+        	beq	zero, zero, finish