diff --git a/Makefile b/Makefile
index 1735ab86..9be0557b 100644
--- a/Makefile
+++ b/Makefile
@@ -31,9 +31,9 @@ VOID = /dev/null
 TARGET_SYSTEM ?= $(OS)
 
 ifneq (,$(filter Windows%,$(TARGET_SYSTEM)))
-EXT =.exe
+  EXT =.exe
 else
-EXT =
+  EXT =
 endif
 
 ## default: Build lib-release and zstd-release
@@ -65,7 +65,7 @@ lib lib-release lib-all :
 .PHONY: zstd zstd-release
 zstd zstd-release:
 	$(Q)$(MAKE) -C $(PRGDIR) $@
-	$(Q)cp $(PRGDIR)/zstd$(EXT) .
+	$(Q)ln -sf $(PRGDIR)/zstd$(EXT) zstd$(EXT)
 
 .PHONY: zstdmt
 zstdmt:
@@ -79,9 +79,9 @@ zlibwrapper: lib
 ## test: run long-duration tests
 .PHONY: test
 DEBUGLEVEL ?= 1
-test: MOREFLAGS += -g -DDEBUGLEVEL=$(DEBUGLEVEL) -Werror
+test: MOREFLAGS += -g -Werror
 test:
-	MOREFLAGS="$(MOREFLAGS)" $(MAKE) -j -C $(PRGDIR) allVariants
+	DEBUGLEVEL=$(DEBUGLEVEL) MOREFLAGS="$(MOREFLAGS)" $(MAKE) -j -C $(PRGDIR) allVariants
 	$(MAKE) -C $(TESTDIR) $@
 	ZSTD=../../programs/zstd $(MAKE) -C doc/educational_decoder $@
 
diff --git a/appveyor.yml b/appveyor.yml
index 91568e48..6b5b9767 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -194,7 +194,7 @@
     - COMPILER: "gcc"
       HOST:     "mingw"
       PLATFORM: "x64"
-      SCRIPT:   "CPPFLAGS=-DDEBUGLEVEL=2 CFLAGS=-Werror make -j allzstd DEBUGLEVEL=2"
+      SCRIPT:   "CFLAGS=-Werror make -j allzstd DEBUGLEVEL=2"
     - COMPILER: "gcc"
       HOST:     "mingw"
       PLATFORM: "x86"
diff --git a/lib/Makefile b/lib/Makefile
index 58e80e47..b8295ff0 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -54,17 +54,18 @@ else
   CFLAGS += -O3
 endif
 
-CPPFLAGS+= -DXXH_NAMESPACE=ZSTD_
+DEBUGLEVEL ?= 0
+CPPFLAGS += -DXXH_NAMESPACE=ZSTD_ -DDEBUGLEVEL=$(DEBUGLEVEL)
 ifeq ($(TARGET_SYSTEM),Windows_NT)   # MinGW assumed
-  CPPFLAGS   += -D__USE_MINGW_ANSI_STDIO   # compatibility with %zu formatting
+  CPPFLAGS += -D__USE_MINGW_ANSI_STDIO   # compatibility with %zu formatting
 endif
 DEBUGFLAGS= -Wall -Wextra -Wcast-qual -Wcast-align -Wshadow \
             -Wstrict-aliasing=1 -Wswitch-enum -Wdeclaration-after-statement \
             -Wstrict-prototypes -Wundef -Wpointer-arith \
             -Wvla -Wformat=2 -Winit-self -Wfloat-equal -Wwrite-strings \
             -Wredundant-decls -Wmissing-prototypes -Wc++-compat
-CFLAGS  += $(DEBUGFLAGS) $(MOREFLAGS)
-FLAGS    = $(CPPFLAGS) $(CFLAGS)
+CFLAGS   += $(DEBUGFLAGS) $(MOREFLAGS)
+FLAGS     = $(CPPFLAGS) $(CFLAGS)
 
 HAVE_COLORNEVER = $(shell echo a | grep --color=never a > /dev/null 2> /dev/null && echo 1 || echo 0)
 GREP_OPTIONS ?=
@@ -170,7 +171,29 @@ ZSTD_LOCAL_OBJ := $(ZSTD_LOCAL_SRC:.c=.o)
 ZSTD_SUBDIR := common compress decompress dictBuilder legacy deprecated
 vpath %.c $(ZSTD_SUBDIR)
 
-BUILD_DIR ?= obj
+UNAME := $(shell uname)
+ifeq ($(UNAME), Darwin)
+  HASH ?= md5
+endif
+ifeq ($(UNAME), FreeBSD)
+  HASH ?= gmd5sum
+endif
+ifeq ($(UNAME), OpenBSD)
+  HASH ?= md5
+endif
+HASH ?= md5sum
+
+HAVE_HASH := $(shell echo 1 | $(HASH) > /dev/null && echo 1 || echo 0)
+ifeq ($(HAVE_HASH), 1)
+  HASH_VALUE := $(shell echo $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $(ZSTD_FILES) | $(HASH) | head -c 16)
+  HASH_DIR := conf_$(HASH_VALUE)
+else
+  $(info warning : could not find hash function to differentiate builds with different flags)
+  HASH_DIR := 0
+endif
+
+
+BUILD_DIR ?= obj/$(HASH_DIR)
 ZSTD_DYNLIB_DIR := $(BUILD_DIR)/dynlib
 ZSTD_DYNLIB_OBJ := $(addprefix $(ZSTD_DYNLIB_DIR)/, $(ZSTD_LOCAL_OBJ))
 ZSTD_STATLIB_DIR := $(BUILD_DIR)/statlib
@@ -178,7 +201,7 @@ ZSTD_STATLIB_OBJ := $(addprefix $(ZSTD_STATLIB_DIR)/, $(ZSTD_LOCAL_OBJ))
 
 # macOS linker doesn't support -soname, and use different extension
 # see : https://developer.apple.com/library/mac/documentation/DeveloperTools/Conceptual/DynamicLibraries/100-Articles/DynamicLibraryDesignGuidelines.html
-ifeq ($(shell uname), Darwin)
+ifeq ($(UNAME), Darwin)
   SHARED_EXT = dylib
   SHARED_EXT_MAJOR = $(LIBVER_MAJOR).$(SHARED_EXT)
   SHARED_EXT_VER = $(LIBVER).$(SHARED_EXT)
@@ -200,14 +223,20 @@ lib-all: all
 
 all: lib
 
-libzstd.a: ARFLAGS = rcs
-libzstd.a: $(ZSTD_STATLIB_OBJ)
+$(ZSTD_STATLIB_DIR)/libzstd.a: ARFLAGS = rcs
+$(ZSTD_STATLIB_DIR)/libzstd.a: | $(ZSTD_STATLIB_DIR)
+$(ZSTD_STATLIB_DIR)/libzstd.a: $(ZSTD_STATLIB_OBJ)
 	@echo compiling static library
 	$(Q)$(AR) $(ARFLAGS) $@ $^
 
+.PHONY: libzstd.a  # must be run every time
+libzstd.a: $(ZSTD_STATLIB_DIR)/libzstd.a
+	$(Q)ln -sf $< $@
+
 ifneq (,$(filter Windows%,$(TARGET_SYSTEM)))
 
 LIBZSTD = dll\libzstd.dll
+$(LIBZSTD):
 $(LIBZSTD): $(ZSTD_FILES)
 	@echo compiling dynamic library $(LIBVER)
 	$(CC) $(FLAGS) -DZSTD_DLL_EXPORT=1 -Wl,--out-implib,dll\libzstd.dll.a -shared $^ -o $@
@@ -215,15 +244,20 @@ $(LIBZSTD): $(ZSTD_FILES)
 else
 
 LIBZSTD = libzstd.$(SHARED_EXT_VER)
-$(LIBZSTD): CFLAGS += -fPIC
-$(LIBZSTD): LDFLAGS += -shared -fvisibility=hidden
-$(LIBZSTD): $(ZSTD_DYNLIB_OBJ)
+$(ZSTD_DYNLIB_DIR)/$(LIBZSTD): CFLAGS += -fPIC
+$(ZSTD_DYNLIB_DIR)/$(LIBZSTD): LDFLAGS += -shared -fvisibility=hidden
+$(ZSTD_DYNLIB_DIR)/$(LIBZSTD): | $(ZSTD_DYNLIB_DIR)
+$(ZSTD_DYNLIB_DIR)/$(LIBZSTD): $(ZSTD_DYNLIB_OBJ)
 	@echo compiling dynamic library $(LIBVER)
 	$(Q)$(CC) $(FLAGS) $^ $(LDFLAGS) $(SONAME_FLAGS) -o $@
 	@echo creating versioned links
 	$(Q)ln -sf $@ libzstd.$(SHARED_EXT_MAJOR)
 	$(Q)ln -sf $@ libzstd.$(SHARED_EXT)
 
+.PHONY: $(LIBZSTD)  # must be run every time
+$(LIBZSTD): $(ZSTD_DYNLIB_DIR)/$(LIBZSTD)
+	$(Q)ln -sf $< $@
+
 endif
 
 .PHONY: libzstd
@@ -281,14 +315,13 @@ clean:
 	$(Q)$(RM) -r *.dSYM   # macOS-specific
 	$(Q)$(RM) core *.o *.a *.gcda *.$(SHARED_EXT) *.$(SHARED_EXT).* libzstd.pc
 	$(Q)$(RM) dll/libzstd.dll dll/libzstd.lib libzstd-nomt*
-	$(Q)$(RM) common/*.o compress/*.o decompress/*.o dictBuilder/*.o legacy/*.o deprecated/*.o
-	$(Q)$(RM) -r $(ZSTD_STATLIB_DIR)/* $(ZSTD_DYNLIB_DIR)/*
+	$(Q)$(RM) -r obj/*
 	@echo Cleaning library completed
 
 #-----------------------------------------------------------------------------
 # make install is validated only for below listed environments
 #-----------------------------------------------------------------------------
-ifneq (,$(filter $(shell uname),Linux Darwin GNU/kFreeBSD GNU OpenBSD FreeBSD NetBSD DragonFly SunOS Haiku))
+ifneq (,$(filter $(UNAME),Linux Darwin GNU/kFreeBSD GNU OpenBSD FreeBSD NetBSD DragonFly SunOS Haiku))
 
 all: libzstd.pc
 
@@ -324,13 +357,13 @@ $(error configured includedir ($(INCLUDEDIR)) is outside of exec_prefix ($(PREFI
 endif
 endif
 
-ifneq (,$(filter $(shell uname),FreeBSD NetBSD DragonFly))
+ifneq (,$(filter $(UNAME),FreeBSD NetBSD DragonFly))
   PKGCONFIGDIR ?= $(PREFIX)/libdata/pkgconfig
 else
   PKGCONFIGDIR ?= $(LIBDIR)/pkgconfig
 endif
 
-ifneq (,$(filter $(shell uname),SunOS))
+ifneq (,$(filter $(UNAME),SunOS))
   INSTALL ?= ginstall
 else
   INSTALL ?= install
diff --git a/lib/README.md b/lib/README.md
index ff62b668..db9170a7 100644
--- a/lib/README.md
+++ b/lib/README.md
@@ -168,6 +168,26 @@ file it should be linked with `dll\libzstd.dll`. For example:
 The compiled executable will require ZSTD DLL which is available at `dll\libzstd.dll`.
 
 
+#### Advanced Build options
+
+The build system requires a hash function in order to
+separate object files created with different compilation flags.
+By default, it tries to use `md5sum` or equivalent.
+The hash function can be manually switched by setting the `HASH` variable.
+For example : `make HASH=xxhsum`
+The hash function needs to generate at least 64-bit using hexadecimal format.
+When no hash function is found,
+the Makefile just generates all object files into the same default directory,
+irrespective of compilation flags.
+This functionality only matters if `libzstd` is compiled multiple times
+with different build flags.
+
+The build directory, where object files are stored
+can also be manually controlled using variable `BUILD_DIR`,
+for example `make BUILD_DIR=objectDir/v1`.
+In which case, the hash function doesn't matter.
+
+
 #### Deprecated API
 
 Obsolete API on their way out are stored in directory `lib/deprecated`.
diff --git a/programs/Makefile b/programs/Makefile
index 8f14292f..70fb2c32 100644
--- a/programs/Makefile
+++ b/programs/Makefile
@@ -36,19 +36,20 @@ ZSTD_VERSION = $(LIBVER)
 HAVE_COLORNEVER = $(shell echo a | grep --color=never a > /dev/null 2> /dev/null && echo 1 || echo 0)
 GREP_OPTIONS ?=
 ifeq ($HAVE_COLORNEVER, 1)
-GREP_OPTIONS += --color=never
+  GREP_OPTIONS += --color=never
 endif
 GREP = grep $(GREP_OPTIONS)
 
 ifeq ($(shell $(CC) -v 2>&1 | $(GREP) -c "gcc version "), 1)
-ALIGN_LOOP = -falign-loops=32
+  ALIGN_LOOP = -falign-loops=32
 else
-ALIGN_LOOP =
+  ALIGN_LOOP =
 endif
 
-CPPFLAGS += -DXXH_NAMESPACE=ZSTD_
+DEBUGLEVEL ?= 0
+CPPFLAGS += -DXXH_NAMESPACE=ZSTD_ -DDEBUGLEVEL=$(DEBUGLEVEL)
 ifeq ($(OS),Windows_NT)   # MinGW assumed
-CPPFLAGS += -D__USE_MINGW_ANSI_STDIO   # compatibility with %zu formatting
+  CPPFLAGS += -D__USE_MINGW_ANSI_STDIO   # compatibility with %zu formatting
 endif
 CFLAGS   ?= -O3
 DEBUGFLAGS+=-Wall -Wextra -Wcast-qual -Wcast-align -Wshadow \
@@ -65,11 +66,7 @@ ZSTDLIB_DECOMPRESS := $(ZSTDDIR)/decompress
 ZDICT_DIR := $(ZSTDDIR)/dictBuilder
 ZSTDLEGACY_DIR := $(ZSTDDIR)/legacy
 
-vpath %.c $(ZSTDLIB_COMMON)
-vpath %.c $(ZSTDLIB_COMPRESS)
-vpath %.c $(ZSTDLIB_DECOMPRESS)
-vpath %.c $(ZDICT_DIR)
-vpath %.c $(ZSTDLEGACY_DIR)
+vpath %.c $(ZSTDLIB_COMMON) $(ZSTDLIB_COMPRESS) $(ZSTDLIB_DECOMPRESS) $(ZDICT_DIR) $(ZSTDLEGACY_DIR)
 
 ZSTDLIB_COMMON_C := $(wildcard $(ZSTDLIB_COMMON)/*.c)
 ZSTDLIB_COMPRESS_C := $(wildcard $(ZSTDLIB_COMPRESS)/*.c)
@@ -81,7 +78,7 @@ ZSTD_LEGACY_SUPPORT ?= 5
 ZSTDLEGACY_SRC :=
 ifneq ($(ZSTD_LEGACY_SUPPORT), 0)
 ifeq ($(shell test $(ZSTD_LEGACY_SUPPORT) -lt 8; echo $$?), 0)
-	ZSTDLEGACY_SRC += $(shell ls $(ZSTDLEGACY_DIR)/*.c | $(GREP) 'v0[$(ZSTD_LEGACY_SUPPORT)-7]')
+  ZSTDLEGACY_SRC += $(shell ls $(ZSTDLEGACY_DIR)/*.c | $(GREP) 'v0[$(ZSTD_LEGACY_SUPPORT)-7]')
 endif
 endif
 
@@ -94,19 +91,44 @@ ZSTD_CLI_SRC := $(wildcard *.c)
 ZSTD_CLI_OBJ := $(ZSTD_CLI_SRC:.c=.o)
 
 ZSTD_ALL_SRC := $(ZSTDLIB_LOCAL_SRC) $(ZSTD_CLI_SRC)
+ZSTD_ALL_OBJ := $(ZSTD_ALL_SRC:.c=.o)
+
+UNAME := $(shell uname)
+ifeq ($(UNAME), Darwin)
+  HASH ?= md5
+endif
+ifeq ($(UNAME), FreeBSD)
+  HASH ?= gmd5sum
+endif
+ifeq ($(UNAME), OpenBSD)
+  HASH ?= md5
+endif
+HASH ?= md5sum
+
+HAVE_HASH := $(shell echo 1 | $(HASH) > /dev/null && echo 1 || echo 0)
+ifeq ($(HAVE_HASH), 1)
+  HASH_VALUE := $(shell echo $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) | $(HASH) | head -c 16)
+  HASH_DIR := conf_$(HASH_VALUE)
+else
+  $(info warning : could not find hash function to differentiate builds with different flags)
+  HASH_DIR := 0
+endif
+
+BUILD_DIR ?= obj/$(HASH_DIR)
+ZSTD_OBJ := $(addprefix $(BUILD_DIR)/, $(ZSTD_ALL_OBJ))
 
 # Define *.exe as extension for Windows systems
 ifneq (,$(filter Windows%,$(OS)))
-EXT =.exe
-RES64_FILE = windres/zstd64.res
-RES32_FILE = windres/zstd32.res
+  EXT =.exe
+  RES64_FILE = windres/zstd64.res
+  RES32_FILE = windres/zstd32.res
 ifneq (,$(filter x86_64%,$(shell $(CC) -dumpmachine)))
     RES_FILE = $(RES64_FILE)
 else
     RES_FILE = $(RES32_FILE)
 endif
 else
-EXT =
+  EXT =
 endif
 
 VOID = /dev/null
@@ -119,54 +141,54 @@ NO_THREAD_MSG := ==> no threads, building without multithreading support
 HAVE_PTHREAD := $(shell printf '$(NUM_SYMBOL)include <pthread.h>\nint main(void) { return 0; }' > have_pthread.c && $(CC) $(FLAGS) -o have_pthread$(EXT) have_pthread.c -pthread 2> $(VOID) && rm have_pthread$(EXT) && echo 1 || echo 0; rm have_pthread.c)
 HAVE_THREAD := $(shell [ "$(HAVE_PTHREAD)" -eq "1" -o -n "$(filter Windows%,$(OS))" ] && echo 1 || echo 0)
 ifeq ($(HAVE_THREAD), 1)
-THREAD_MSG := ==> building with threading support
-THREAD_CPP := -DZSTD_MULTITHREAD
-THREAD_LD := -pthread
+  THREAD_MSG := ==> building with threading support
+  THREAD_CPP := -DZSTD_MULTITHREAD
+  THREAD_LD := -pthread
 else
-THREAD_MSG := $(NO_THREAD_MSG)
+  THREAD_MSG := $(NO_THREAD_MSG)
 endif
 
 # zlib detection
 NO_ZLIB_MSG := ==> no zlib, building zstd without .gz support
 HAVE_ZLIB := $(shell printf '$(NUM_SYMBOL)include <zlib.h>\nint main(void) { return 0; }' > have_zlib.c && $(CC) $(FLAGS) -o have_zlib$(EXT) have_zlib.c -lz 2> $(VOID) && rm have_zlib$(EXT) && echo 1 || echo 0; rm have_zlib.c)
 ifeq ($(HAVE_ZLIB), 1)
-ZLIB_MSG := ==> building zstd with .gz compression support
-ZLIBCPP = -DZSTD_GZCOMPRESS -DZSTD_GZDECOMPRESS
-ZLIBLD = -lz
+  ZLIB_MSG := ==> building zstd with .gz compression support
+  ZLIBCPP = -DZSTD_GZCOMPRESS -DZSTD_GZDECOMPRESS
+  ZLIBLD = -lz
 else
-ZLIB_MSG := $(NO_ZLIB_MSG)
+  ZLIB_MSG := $(NO_ZLIB_MSG)
 endif
 
 # lzma detection
 NO_LZMA_MSG := ==> no liblzma, building zstd without .xz/.lzma support
 HAVE_LZMA := $(shell printf '$(NUM_SYMBOL)include <lzma.h>\nint main(void) { return 0; }' > have_lzma.c && $(CC) $(FLAGS) -o have_lzma$(EXT) have_lzma.c -llzma 2> $(VOID) && rm have_lzma$(EXT) && echo 1 || echo 0; rm have_lzma.c)
 ifeq ($(HAVE_LZMA), 1)
-LZMA_MSG := ==> building zstd with .xz/.lzma compression support
-LZMACPP = -DZSTD_LZMACOMPRESS -DZSTD_LZMADECOMPRESS
-LZMALD = -llzma
+  LZMA_MSG := ==> building zstd with .xz/.lzma compression support
+  LZMACPP = -DZSTD_LZMACOMPRESS -DZSTD_LZMADECOMPRESS
+  LZMALD = -llzma
 else
-LZMA_MSG := $(NO_LZMA_MSG)
+  LZMA_MSG := $(NO_LZMA_MSG)
 endif
 
 # lz4 detection
 NO_LZ4_MSG := ==> no liblz4, building zstd without .lz4 support
 HAVE_LZ4 := $(shell printf '$(NUM_SYMBOL)include <lz4frame.h>\n$(NUM_SYMBOL)include <lz4.h>\nint main(void) { return 0; }' > have_lz4.c && $(CC) $(FLAGS) -o have_lz4$(EXT) have_lz4.c -llz4 2> $(VOID) && rm have_lz4$(EXT) && echo 1 || echo 0; rm have_lz4.c)
 ifeq ($(HAVE_LZ4), 1)
-LZ4_MSG := ==> building zstd with .lz4 compression support
-LZ4CPP = -DZSTD_LZ4COMPRESS -DZSTD_LZ4DECOMPRESS
-LZ4LD = -llz4
+  LZ4_MSG := ==> building zstd with .lz4 compression support
+  LZ4CPP = -DZSTD_LZ4COMPRESS -DZSTD_LZ4DECOMPRESS
+  LZ4LD = -llz4
 else
-LZ4_MSG := $(NO_LZ4_MSG)
+  LZ4_MSG := $(NO_LZ4_MSG)
 endif
 
 # explicit backtrace enable/disable for Linux & Darwin
 ifeq ($(BACKTRACE), 0)
-DEBUGFLAGS += -DBACKTRACE_ENABLE=0
+  DEBUGFLAGS += -DBACKTRACE_ENABLE=0
 endif
 ifeq (,$(filter Windows%, $(OS)))
 ifeq ($(BACKTRACE), 1)
-DEBUGFLAGS += -DBACKTRACE_ENABLE=1
-DEBUGFLAGS_LD += -rdynamic
+  DEBUGFLAGS += -DBACKTRACE_ENABLE=1
+  DEBUGFLAGS_LD += -rdynamic
 endif
 endif
 
@@ -180,18 +202,23 @@ all: zstd
 .PHONY: allVariants
 allVariants: zstd zstd-compress zstd-decompress zstd-small zstd-nolegacy zstd-dictBuilder
 
+$(BUILD_DIR)/zstd : $(ZSTD_OBJ)
+	@echo "$(THREAD_MSG)"
+	@echo "$(ZLIB_MSG)"
+	@echo "$(LZMA_MSG)"
+	@echo "$(LZ4_MSG)"
+	$(Q)$(CC) $(FLAGS) $^ -o $@$(EXT) $(LDFLAGS)
+
+.PHONY: zstd
 zstd : CPPFLAGS += $(THREAD_CPP) $(ZLIBCPP) $(LZMACPP) $(LZ4CPP)
 zstd : LDFLAGS += $(THREAD_LD) $(ZLIBLD) $(LZMALD) $(LZ4LD) $(DEBUGFLAGS_LD)
 zstd : CPPFLAGS += -DZSTD_LEGACY_SUPPORT=$(ZSTD_LEGACY_SUPPORT)
 ifneq (,$(filter Windows%,$(OS)))
 zstd : $(RES_FILE)
 endif
-zstd : $(ZSTDLIB_LOCAL_OBJ) $(ZSTD_CLI_OBJ)
-	@echo "$(THREAD_MSG)"
-	@echo "$(ZLIB_MSG)"
-	@echo "$(LZMA_MSG)"
-	@echo "$(LZ4_MSG)"
-	$(CC) $(FLAGS) $^ -o $@$(EXT) $(LDFLAGS)
+zstd : $(BUILD_DIR)/zstd
+	$(Q)ln -sf $< $@
+	@echo zstd build completed
 
 .PHONY: zstd-release
 zstd-release: DEBUGFLAGS := -DBACKTRACE_ENABLE=0
@@ -292,6 +319,7 @@ clean:
         zstd$(EXT) zstd32$(EXT) zstd-compress$(EXT) zstd-decompress$(EXT) \
         zstd-small$(EXT) zstd-frugal$(EXT) zstd-nolegacy$(EXT) zstd4$(EXT) \
         zstd-dictBuilder$(EXT) *.gcda default*.profraw default.profdata have_zlib$(EXT)
+	$(Q)$(RM) -r obj/*
 	@echo Cleaning completed
 
 MD2ROFF = ronn
@@ -324,34 +352,32 @@ preview-man: clean-man man
 
 # Generate .h dependencies automatically
 
-MKDIR = mkdir
+DEPFLAGS = -MT $@ -MMD -MP -MF
 
-DEPDIR := .deps
-DEPFLAGS = -MT $@ -MMD -MP -MF $(DEPDIR)/$*.d
+$(BUILD_DIR)/%.o : %.c $(BUILD_DIR)/%.d | $(BUILD_DIR)
+	@echo $@
+	$(Q)$(COMPILE.c) $(DEPFLAGS) $(BUILD_DIR)/$*.d $(OUTPUT_OPTION) $<
 
-COMPILE.c = $(CC) $(DEPFLAGS) $(CFLAGS) $(CPPFLAGS) -c
+MKDIR ?= mkdir
+$(BUILD_DIR): ; $(Q)$(MKDIR) -p $@
 
-%.o : %.c
-%.o : %.c $(DEPDIR)/%.d | $(DEPDIR)
-	$(COMPILE.c) $(OUTPUT_OPTION) $<
-
-$(DEPDIR): ; $(Q)$(MKDIR) -p $@
-
-DEPFILES := $(ZSTD_ALL_SRC:%.c=$(DEPDIR)/%.d)
+DEPFILES := $(ZSTD_OBJ:.o=.d)
 $(DEPFILES):
 
 include $(wildcard $(DEPFILES))
 
 
+
 #-----------------------------------------------------------------------------
 # make install is validated only for Linux, macOS, BSD, Hurd and Solaris targets
 #-----------------------------------------------------------------------------
-ifneq (,$(filter $(shell uname),Linux Darwin GNU/kFreeBSD GNU OpenBSD FreeBSD NetBSD DragonFly SunOS Haiku))
+UNAME := $(shell uname)
+ifneq (,$(filter $(UNAME),Linux Darwin GNU/kFreeBSD GNU OpenBSD FreeBSD NetBSD DragonFly SunOS Haiku))
 
 HAVE_COLORNEVER = $(shell echo a | egrep --color=never a > /dev/null 2> /dev/null && echo 1 || echo 0)
 EGREP_OPTIONS ?=
 ifeq ($HAVE_COLORNEVER, 1)
-EGREP_OPTIONS += --color=never
+  EGREP_OPTIONS += --color=never
 endif
 EGREP = egrep $(EGREP_OPTIONS)
 AWK = awk
@@ -389,17 +415,17 @@ datarootdir ?= $(PREFIX)/share
 mandir      ?= $(datarootdir)/man
 man1dir     ?= $(mandir)/man1
 
-ifneq (,$(filter $(shell uname),OpenBSD FreeBSD NetBSD DragonFly SunOS))
-MANDIR  ?= $(PREFIX)/man
-MAN1DIR ?= $(MANDIR)/man1
+ifneq (,$(filter $(UNAME),OpenBSD FreeBSD NetBSD DragonFly SunOS))
+  MANDIR  ?= $(PREFIX)/man
+  MAN1DIR ?= $(MANDIR)/man1
 else
-MAN1DIR ?= $(man1dir)
+  MAN1DIR ?= $(man1dir)
 endif
 
-ifneq (,$(filter $(shell uname),SunOS))
-INSTALL ?= ginstall
+ifneq (,$(filter $(UNAME),SunOS))
+  INSTALL ?= ginstall
 else
-INSTALL ?= install
+  INSTALL ?= install
 endif
 
 INSTALL_PROGRAM ?= $(INSTALL)
diff --git a/programs/README.md b/programs/README.md
index 53f716bd..cf7f5ba4 100644
--- a/programs/README.md
+++ b/programs/README.md
@@ -3,7 +3,7 @@ Command Line Interface for Zstandard library
 
 Command Line Interface (CLI) can be created using the `make` command without any additional parameters.
 There are however other Makefile targets that create different variations of CLI:
-- `zstd` : default CLI supporting gzip-like arguments; includes dictionary builder, benchmark, and support for decompression of legacy zstd formats
+- `zstd` : default CLI supporting gzip-like arguments; includes dictionary builder, benchmark, and supports decompression of legacy zstd formats
 - `zstd_nolegacy` : Same as `zstd` but without support for legacy zstd formats
 - `zstd-small` : CLI optimized for minimal size; no dictionary builder, no benchmark, and no support for legacy zstd formats
 - `zstd-compress` : version of CLI which can only compress into zstd format
@@ -147,76 +147,91 @@ FILE    : a filename
 Arguments :
  -#     : # compression level (1-19, default: 3)
  -d     : decompression
- -D file: use `file` as Dictionary
- -o file: result stored into `file` (only if 1 input file)
- -f     : overwrite output without prompting and (de)compress links
+ -D DICT: use DICT as Dictionary for compression or decompression
+ -o file: result stored into `file` (only 1 output file)
+ -f     : overwrite output without prompting, also (de)compress links
 --rm    : remove source file(s) after successful de/compression
  -k     : preserve source file(s) (default)
  -h/-H  : display help/long help and exit
 
 Advanced arguments :
  -V     : display Version number and exit
+ -c     : force write to standard output, even if it is the console
  -v     : verbose mode; specify multiple times to increase verbosity
  -q     : suppress warnings; specify twice to suppress errors too
- -c     : force write to standard output, even if it is the console
- -l     : print information about zstd compressed files
---exclude-compressed:  only compress files that are not previously compressed
+--no-progress : do not display the progress counter
+ -r     : operate recursively on directories
+--filelist FILE : read list of files to operate upon from FILE
+--output-dir-flat DIR : processed files are stored into DIR
+--output-dir-mirror DIR : processed files are stored into DIR respecting original directory structure
+--[no-]check : during compression, add XXH64 integrity checksum to frame (default: enabled). If specified with -d, decompressor will ignore/validate checksums in compressed frame (default: validate).
+--      : All arguments after "--" are treated as files
+
+Advanced compression arguments :
 --ultra : enable levels beyond 19, up to 22 (requires more memory)
 --long[=#]: enable long distance matching with given window log (default: 27)
 --fast[=#]: switch to very fast compression levels (default: 1)
 --adapt : dynamically adapt compression level to I/O conditions
---stream-size=# : optimize compression parameters for streaming input of given number of bytes
---size-hint=# optimize compression parameters for streaming input of approximately this size
---target-compressed-block-size=# : make compressed block near targeted size
  -T#    : spawns # compression threads (default: 1, 0==# cores)
  -B#    : select size of each job (default: 0==automatic)
+--single-thread : use a single thread for both I/O and compression (result slightly different than -T1)
 --rsyncable : compress using a rsync-friendly method (-B sets block size)
---no-dictID : don't write dictID into header (dictionary compression)
---[no-]check : integrity check (default: enabled)
+--exclude-compressed: only compress files that are not already compressed
+--stream-size=# : specify size of streaming input from `stdin`
+--size-hint=# optimize compression parameters for streaming input of approximately this size
+--target-compressed-block-size=# : generate compressed block of approximately targeted size
+--no-dictID : don't write dictID into header (dictionary compression only)
 --[no-]compress-literals : force (un)compressed literals
- -r     : operate recursively on directories
---output-dir-flat[=directory]: all resulting files stored into `directory`.
 --format=zstd : compress files to the .zst format (default)
 --format=gzip : compress files to the .gz format
+--format=xz : compress files to the .xz format
+--format=lzma : compress files to the .lzma format
+--format=lz4 : compress files to the .lz4 format
+
+Advanced decompression arguments :
+ -l     : print information about zstd compressed files
 --test  : test compressed file integrity
---[no-]sparse : sparse mode (default: disabled)
  -M#    : Set a memory usage limit for decompression
---no-progress : do not display the progress bar
---      : All arguments after "--" are treated as files
+--[no-]sparse : sparse mode (default: disabled)
 
 Dictionary builder :
 --train ## : create a dictionary from a training set of files
 --train-cover[=k=#,d=#,steps=#,split=#,shrink[=#]] : use the cover algorithm with optional args
 --train-fastcover[=k=#,d=#,f=#,steps=#,split=#,accel=#,shrink[=#]] : use the fast cover algorithm with optional args
 --train-legacy[=s=#] : use the legacy algorithm with selectivity (default: 9)
- -o file : `file` is dictionary name (default: dictionary)
+ -o DICT : DICT is dictionary name (default: dictionary)
 --maxdict=# : limit dictionary to specified size (default: 112640)
 --dictID=# : force dictionary ID to specified value (default: random)
 
 Benchmark arguments :
  -b#    : benchmark file(s), using # compression level (default: 3)
- -e#    : test all compression levels from -bX to # (default: 1)
+ -e#    : test all compression levels successively from -b# to -e# (default: 1)
  -i#    : minimum evaluation time in seconds (default: 3s)
  -B#    : cut file into independent blocks of size # (default: no block)
+ -S     : output one benchmark result per input file (default: consolidated result)
 --priority=rt : set process priority to real-time
 ```
 
 ### Passing parameters through Environment Variables
+There is no "generic" way to pass "any kind of parameter" to `zstd` in a pass-through manner.
+Using environment variables for this purpose has security implications.
+Therefore, this avenue is intentionally restricted and only supports `ZSTD_CLEVEL` and `ZSTD_NBTHREADS`.
+
 `ZSTD_CLEVEL` can be used to modify the default compression level of `zstd`
 (usually set to `3`) to another value between 1 and 19 (the "normal" range).
-`ZSTD_NBTHREADS` can be used to specify number of threads that `zstd` will use during compression, which by default is `1`.
+
+`ZSTD_NBTHREADS` can be used to specify a number of threads
+that `zstd` will use for compression, which by default is `1`.
 This functionality only exists when `zstd` is compiled with multithread support.
+`0` means "use as many threads as detected cpu cores on local system".
 The max # of threads is capped at: `ZSTDMT_NBWORKERS_MAX==200`.
 
 This functionality can be useful when `zstd` CLI is invoked in a way that doesn't allow passing arguments.
 One such scenario is `tar --zstd`.
 As `ZSTD_CLEVEL` and `ZSTD_NBTHREADS` only replace the default compression level
-and number of threads, respectively, they can both be overridden by corresponding command line arguments:
+and number of threads respectively, they can both be overridden by corresponding command line arguments:
 `-#` for compression level and `-T#` for number of threads.
 
-There is no "generic" way to pass "any kind of parameter" to `zstd` in a pass-through manner.
-Using environment variables for this purpose has security implications.
-Therefore, this avenue is intentionally restricted and only supports `ZSTD_CLEVEL` and `ZSTD_NBTHREADS`.
 
 ### Long distance matching mode
 The long distance matching mode, enabled with `--long`, is designed to improve
diff --git a/tests/Makefile b/tests/Makefile
index d347a948..c39c5ca0 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -94,23 +94,23 @@ allnothread: fullbench fuzzer paramgrill datagen decodecorpus
 # note : broken : requires symbols unavailable from dynamic library
 dll: fuzzer-dll zstreamtest-dll
 
-PHONY: zstd zstd32 zstd-nolegacy  # must be phony, only external makefile knows how to build them, or if they need an update
+PHONY: zstd zstd32 zstd-nolegacy  # phony: only external makefile knows how to build or update them
 zstd zstd32 zstd-nolegacy:
-	$(MAKE) -C $(PRGDIR) $@ MOREFLAGS+="$(DEBUGFLAGS)"
+	$(MAKE) -C $(PRGDIR) $@ MOREFLAGS+="$(DEBUGFLAGS)" DEBUGLEVEL=$(DEBUGLEVEL)
 
 gzstd:
-	$(MAKE) -C $(PRGDIR) $@ HAVE_ZLIB=1 MOREFLAGS+="$(DEBUGFLAGS)"
+	$(MAKE) -C $(PRGDIR) $@ HAVE_ZLIB=1 MOREFLAGS+="$(DEBUGFLAGS)" DEBUGLEVEL=$(DEBUGLEVEL)
 
 .PHONY: libzstd
 libzstd :
-	$(MAKE) -C $(ZSTDDIR) libzstd
+	$(MAKE) -C $(ZSTDDIR) libzstd DEBUGLEVEL=$(DEBUGLEVEL)
 
 %-dll : libzstd
 %-dll : LDFLAGS+= -L$(ZSTDDIR) -lzstd
 
 .PHONY: zstd-staticLib
 zstd-staticLib :
-	$(MAKE) -C $(ZSTDDIR) libzstd.a
+	$(MAKE) -C $(ZSTDDIR) libzstd.a DEBUGLEVEL=$(DEBUGLEVEL)
 
 zstdm_%.o : $(ZSTDDIR)/common/%.c
 	$(CC) -c $(CPPFLAGS) $(CFLAGS) $< -o $@
@@ -255,7 +255,8 @@ clean:
 #----------------------------------------------------------------------------------
 # valgrind tests are validated only for some posix platforms
 #----------------------------------------------------------------------------------
-ifneq (,$(filter $(shell uname),Linux Darwin GNU/kFreeBSD GNU OpenBSD FreeBSD NetBSD DragonFly SunOS))
+UNAME := $(shell uname)
+ifneq (,$(filter $(UNAME),Linux Darwin GNU/kFreeBSD GNU OpenBSD FreeBSD NetBSD DragonFly SunOS))
 HOST_OS = POSIX
 
 valgrindTest: VALGRIND = valgrind --leak-check=full --show-leak-kinds=all --error-exitcode=1
@@ -275,8 +276,8 @@ valgrindTest: zstd datagen fuzzer fullbench
 endif
 
 
-ifneq (,$(filter MINGW% MSYS%,$(shell uname)))
-HOST_OS = MSYS
+ifneq (,$(filter MINGW% MSYS%,$(UNAME)))
+  HOST_OS = MSYS
 endif
 
 
@@ -286,8 +287,8 @@ endif
 ifneq (,$(filter $(HOST_OS),MSYS POSIX))
 
 DIFF:=diff
-ifneq (,$(filter $(shell uname),SunOS))
-DIFF:=gdiff
+ifneq (,$(filter $(UNAME),SunOS))
+  DIFF:=gdiff
 endif
 
 .PHONY: list
diff --git a/tests/libzstd_partial_builds.sh b/tests/libzstd_partial_builds.sh
index b1c1e3b1..bee2dbda 100755
--- a/tests/libzstd_partial_builds.sh
+++ b/tests/libzstd_partial_builds.sh
@@ -22,7 +22,6 @@ mustBeAbsent() {
 }
 
 # default compilation : all features enabled
-make clean > /dev/null
 $ECHO "testing default library compilation"
 CFLAGS= make -C $DIR/../lib libzstd.a > $INTOVOID
 nm $DIR/../lib/libzstd.a | $GREP "\.o" > tmplog