wasm: Add a wasm liblc3 library

The wasm library is automatically built when the compiler target
is set to wasm32 in bin/liblc3.wasm.

This can be done using `make CC="clang --target=wasm32"`.

This wasm library doesn't have any import and expose all liblc3
functions.

Makefile

@@ -33,6 +33,16 @@ LDFLAGS := $(if $(DEBUG),-O0 -g,-O3)
 
 CFLAGS += -std=c11 -Wall -Wextra -Wdouble-promotion -Wvla -pedantic
 
+TARGET = $(lastword $(shell $(CC) -v 2>&1 | grep "Target: "))
+
+LIB_SUFFIX := so
+
+ifeq ($(TARGET),wasm32)
+  LIB_SUFFIX := wasm
+  CFLAGS += -mbulk-memory
+  LDFLAGS += -nostdlib -Wl,--no-entry -Wl,--export-dynamic
+endif
+
 ifneq ($(LC3_PLUS),)
   DEFINE += LC3_PLUS=$(LC3_PLUS)
 endif
@@ -50,7 +60,7 @@ lib_list :=
 bin_list :=
 
 define add-lib
-    $(eval $(1)_bin ?= $(1).so)
+    $(eval $(1)_bin ?= $(1).$(LIB_SUFFIX))
     $(eval $(1)_bin := $(addprefix $(BIN_DIR)/,$($(1)_bin)))
 
     lib_list += $(1)

src/common.h

@@ -24,7 +24,15 @@
 
 #include <stdalign.h>
 #include <limits.h>
+
+#ifdef __wasm32__
+#define memmove __builtin_memmove
+#define memset __builtin_memset
+#define memcpy __builtin_memcpy
+#define NULL ((void*)0)
+#else
 #include <string.h>
+#endif
 
 #ifdef __ARM_ARCH
 #include <arm_acle.h>

src/fastmath.h

@@ -20,7 +20,26 @@
 #define __LC3_FASTMATH_H
 
 #include <stdint.h>
+
+#ifdef __wasm32__
+#define log10f __builtin_log10f
+#define sqrtf __builtin_sqrtf
+#define fabsf __builtin_fabsf
+#define floorf __builtin_floorf
+#define fminf __builtin_fminf
+#define fmaxf __builtin_fmaxf
+#define truncf __builtin_truncf
+// This is not exactly roundf, as this return the even value for two equally near
+// values. e.g
+// - roundf(0.5) = 1, nearbyint(0.5) = 0,
+// - roundf(1.5) = 2, nearbyint(1.5) = 2,
+// - roundf(2.5) = 3, nearbyint(2.5) = 2
+// but this builtin maps to https://webassembly.github.io/spec/core/exec/numerics.html#op-fnearest
+#define roundf __builtin_nearbyint
+#define INFINITY __builtin_inff()
+#else
 #include <math.h>
+#endif
 
 
 /**