Auto-download FFTW source for Android build

Makefile.android now downloads fftw-3.3.11.tar.gz automatically instead
of requiring the user to place sources in third_party/fftw/ manually.
The FFTW_SRC variable can still be overridden to use an existing copy.
Added distclean target. Updated README accordingly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Makefile.android

@@ -5,9 +5,8 @@
 # Optional overrides:
 #   ANDROID_NDK=/path/to/ndk ANDROID_API=24 ANDROID_ABIS="arm64-v8a x86_64"
 #
-# Requires FFTW source in third_party/fftw/
-#   Download from https://www.fftw.org/download.html and extract so that
-#   third_party/fftw/configure exists.
+# FFTW source is downloaded and extracted automatically.
+# Override FFTW_SRC to use an existing directory.
 
 ANDROID_NDK ?= /home/vladimir/Android/Sdk/ndk/29.0.14206865
 ANDROID_API ?= 24
@@ -24,7 +23,10 @@ COMMON_CPPFLAGS ?= -I. -I third_party/rnnoise/include -I third_party/libspecblea
 ANDROID_JNI_CFLAGS ?= -std=gnu89 -Wno-implicit-function-declaration -Wno-int-conversion \
   -Wno-incompatible-pointer-types -Wno-incompatible-pointer-types-discards-qualifiers
 
-FFTW_SRC ?= third_party/fftw
+FFTW_VERSION  := 3.3.11
+FFTW_TAR      := fftw-$(FFTW_VERSION).tar.gz
+FFTW_URL      := https://fftw.org/pub/fftw/$(FFTW_TAR)
+FFTW_SRC      ?= third_party/fftw-$(FFTW_VERSION)
 FFTW_MAKEJOBS ?= $(shell nproc 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || echo 4)
 
 WDSP_SOURCES = amd.c \
@@ -148,9 +150,9 @@ ANDROID_OBJ_ROOT  := obj/android
 ANDROID_LIB_ROOT  := lib/android
 ANDROID_JAVA_OUT  := lib/android/java
 
-.PHONY: all clean java-classes check-fftw-src
+.PHONY: all clean distclean java-classes
 
-all: check-fftw-src \
+all: $(FFTW_SRC)/configure \
   $(foreach abi,$(ANDROID_ABIS),\
     $(ANDROID_LIB_ROOT)/$(abi)/libfftw3.so \
     $(ANDROID_LIB_ROOT)/$(abi)/libfftw3f.so \
@@ -158,15 +160,21 @@ all: check-fftw-src \
     $(ANDROID_LIB_ROOT)/$(abi)/libwdspj.so) \
   java-classes
 
-check-fftw-src:
-	@test -f $(FFTW_SRC)/configure || { \
-	  echo ""; \
-	  echo "ERROR: FFTW source not found at $(FFTW_SRC)/configure"; \
-	  echo "Download and extract FFTW from https://www.fftw.org/download.html"; \
-	  echo "so that $(FFTW_SRC)/configure exists."; \
-	  echo ""; \
-	  exit 1; \
-	}
+# ── Автоматическое получение FFTW ────────────────────────────────────────────
+
+third_party/$(FFTW_TAR):
+	mkdir -p third_party
+	@echo ">>> Скачиваем FFTW $(FFTW_VERSION)..."
+	@if command -v wget >/dev/null 2>&1; then \
+	  wget -q --show-progress -O $@ "$(FFTW_URL)"; \
+	else \
+	  curl -L --progress-bar -o $@ "$(FFTW_URL)"; \
+	fi
+
+$(FFTW_SRC)/configure: third_party/$(FFTW_TAR)
+	@echo ">>> Распаковываем FFTW..."
+	tar xf $< -C third_party/
+	@touch $@
 
 # abi_target: compiler triple for NDK clang wrapper
 define abi_target
@@ -226,7 +234,7 @@ ABI_$(1)_WDSP_OBJS := $$(patsubst %.c,$$(ABI_$(1)_OBJDIR)/%.o,$$(ALL_C_SOURCES))
 ABI_$(1)_JNI_OBJ   := $$(ABI_$(1)_OBJDIR)/$(JNI_SOURCE:.c=.o)
 
 # --- Build fftw3 (double) ---
-$$(ABI_$(1)_FFTW_STAMP):
+$$(ABI_$(1)_FFTW_STAMP): $(FFTW_SRC)/configure
 	@mkdir -p $$(ABI_$(1)_OBJDIR)/fftw-build $$(ABI_$(1)_FFTW_PREFIX)
 	cd $$(ABI_$(1)_OBJDIR)/fftw-build && \
 	  $(abspath $(FFTW_SRC))/configure \
@@ -240,7 +248,7 @@ $$(ABI_$(1)_FFTW_STAMP):
 	@touch $$@
 
 # --- Build fftw3f (float/single) ---
-$$(ABI_$(1)_FFTWF_STAMP):
+$$(ABI_$(1)_FFTWF_STAMP): $(FFTW_SRC)/configure
 	@mkdir -p $$(ABI_$(1)_OBJDIR)/fftwf-build $$(ABI_$(1)_FFTWF_PREFIX)
 	cd $$(ABI_$(1)_OBJDIR)/fftwf-build && \
 	  $(abspath $(FFTW_SRC))/configure \
@@ -311,3 +319,6 @@ java-classes: $(JAVA_SOURCE)
 
 clean:
 	rm -rf $(ANDROID_OBJ_ROOT) $(ANDROID_LIB_ROOT)
+
+distclean: clean
+	-rm -rf $(FFTW_SRC) third_party/$(FFTW_TAR)