add Makefile patches to README

diff --git a/README.md b/README.md
index dc09b92c64d641b3b8945e8469c4ffa3d734e454..d219864a341e4b656680de476e385b6a7f70fb9b 100644 (file)
--- a/README.md
+++ b/README.md
@@ -10,8 +10,59 @@ may be used in any project (not limited to one specific processor).
 * yosys (latest git repository, required by nmigen)
 * sfpy (running unit tests).  provides python bindings to berkeley softfloat-3
 
+# Building sfpy
+
+The standard sfpy will not work without being modified to the type of
+IEEE754 FP emulation being tested.  This FPU is emulating RISC-V, and
+there is some weirdness in x86 IEEE754 implementations when it comes
+to FP16 non-canonical NaNs.
+
+The following modifications are required to the sfpy berkeley-softfloat-3
+Makefile:
+
+    diff --git a/build/Linux-x86_64-GCC/Makefile b/build/Linux-x86_64-GCC/Makefile
+    index 2ee5dad..566d225 100644
+    --- a/build/Linux-x86_64-GCC/Makefile
+    +++ b/build/Linux-x86_64-GCC/Makefile
+    @@ -35,7 +35,7 @@
+     #=============================================================================
+     
+     SOURCE_DIR ?= ../../source
+    -SPECIALIZE_TYPE ?= 8086-SSE
+    +SPECIALIZE_TYPE ?= RISCV
+     
+     SOFTFLOAT_OPTS ?= \
+       -DSOFTFLOAT_ROUND_ODD -DINLINE_LEVEL=5 -DSOFTFLOAT_FAST_DIV32TO16 \
+    @@ -45,7 +45,7 @@ DELETE = rm -f
+     C_INCLUDES = -I. -I$(SOURCE_DIR)/$(SPECIALIZE_TYPE) -I$(SOURCE_DIR)/include
+     COMPILE_C = \
+       gcc -c -Werror-implicit-function-declaration -DSOFTFLOAT_FAST_INT64 \
+    -    $(SOFTFLOAT_OPTS) $(C_INCLUDES) -O2 -o $@
+    +    $(SOFTFLOAT_OPTS) $(C_INCLUDES) -O2 -fPIC -o $@
+     MAKELIB = ar crs $@
+     
+     OBJ = .o
+
+
+The following modifications are required to the sfpy SoftPosit Makefile:
+
+    diff --git a/build/Linux-x86_64-GCC/Makefile b/build/Linux-x86_64-GCC/Makefile
+    index 7affd4b..25dd39e 100644
+    --- a/build/Linux-x86_64-GCC/Makefile
+    +++ b/build/Linux-x86_64-GCC/Makefile
+    @@ -69,7 +69,7 @@ endif
+     C_INCLUDES = -I. -I$(SOURCE_DIR)/$(SPECIALIZE_TYPE) -I$(SOURCE_DIR)/include
+     OPTIMISATION  = -O2 #-march=core-avx2
+     COMPILE_C = \
+    -  $(COMPILER) -c -Werror-implicit-function-declaration -DSOFTPOSIT_FAST_INT64 \
+    +  $(COMPILER) -fPIC -c -Werror-implicit-function-declaration -DSOFTPOSIT_FAST_INT64 \
+         $(SOFTPOSIT_OPTS) $(C_INCLUDES) $(OPTIMISATION) \
+         -o $@ 
+     MAKELIB = ar crs $@
+
 # Useful resources
 
 * https://en.wikipedia.org/wiki/IEEE_754-1985
 * http://weitz.de/ieee/
 * https://steve.hollasch.net/cgindex/coding/ieeefloat.html
+