[Cryptech-Commits] [sw/stm32] 01/02: Replace the brutally inefficient fp_to_unsigned_bin with one based on fp_read_unsigned_bin.

[git at cryptech.is]

This is an automated email from the git hooks/post-receive script.

paul at psgd.org pushed a commit to branch master
in repository sw/stm32.

commit 38b388061364339c1259b56fe1d366de8b8630d3
Author: Paul Selkirk <paul at psgd.org>
AuthorDate: Mon Mar 9 15:47:17 2020 -0400

    Replace the brutally inefficient fp_to_unsigned_bin with one based on
    fp_read_unsigned_bin.
    
    I thought about patching it directly in sw/thirdparty/libtfm, but
    ultimately decided to keep that pristine (especially since we verify file
    checksums there).
---
 libraries/libtfm/Makefile             |  7 ++--
 libraries/libtfm/fp_to_unsigned_bin.c | 62 +++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/libraries/libtfm/Makefile b/libraries/libtfm/Makefile
index 34b9314..aa5031f 100644
--- a/libraries/libtfm/Makefile
+++ b/libraries/libtfm/Makefile
@@ -45,10 +45,12 @@ CFLAGS += -Wall -W -Wshadow -Wno-uninitialized
 
 TARGETS	:= $(notdir ${HDR} ${LIB})
 
+REPLACE = fp_to_unsigned_bin.o
+
 all: ${TARGETS}
 
 clean:
-	rm -rf ${TARGETS} $(notdir ${HDR}.tmp) ${LIB} tomsfastmath/src
+	rm -rf ${TARGETS} $(notdir ${HDR}.tmp) ${LIB} tomsfastmath/src ${REPLACE}
 
 distclean: clean
 	rm -f TAGS
@@ -63,6 +65,7 @@ $(notdir ${HDR}): ${HDR}
 $(notdir ${LIB}): ${LIB}
 	ln -f $^ $@
 
-${LIB}: ${HDR}
+${LIB}: ${HDR} ${REPLACE}
 	(cd ${LIBTFM_SRC} && find tomsfastmath/src -type d) | xargs mkdir -p
 	cd tomsfastmath; ${MAKE} CFLAGS='${CFLAGS}'
+	ar r ${LIB} ${REPLACE}
diff --git a/libraries/libtfm/fp_to_unsigned_bin.c b/libraries/libtfm/fp_to_unsigned_bin.c
new file mode 100644
index 0000000..618167d
--- /dev/null
+++ b/libraries/libtfm/fp_to_unsigned_bin.c
@@ -0,0 +1,62 @@
+/* TomsFastMath, a fast ISO C bignum library.
+ * 
+ * This project is meant to fill in where LibTomMath
+ * falls short.  That is speed ;-)
+ *
+ * This project is public domain and free for all purposes.
+ * 
+ * Tom St Denis, tomstdenis at gmail.com
+ */
+#include <tfm_private.h>
+
+void fp_to_unsigned_bin(fp_int *a, unsigned char *b)
+{
+  /* If we know the endianness of this architecture, and we're using
+     32-bit fp_digits, we can optimize this */
+#if (defined(ENDIAN_LITTLE) || defined(ENDIAN_BIG)) && !defined(FP_64BIT)
+  /* But not for both simultaneously */
+#if defined(ENDIAN_LITTLE) && defined(ENDIAN_BIG)
+#error Both ENDIAN_LITTLE and ENDIAN_BIG defined.
+#endif
+  {
+    int c = fp_unsigned_bin_size(a);
+    unsigned char *pd = (unsigned char *)a->dp;
+
+    /* read the bytes out */
+#ifdef ENDIAN_BIG
+    {
+      /* Use Duff's device to unroll the loop. */
+      int idx = (c - 1) & ~3;
+      switch (c % 4) {
+      case 0:	do { b[idx+0] = *pd++;
+      case 3:	     b[idx+1] = *pd++;
+      case 2:	     b[idx+2] = *pd++;
+      case 1:	     b[idx+3] = *pd++;
+                     idx -= 4;
+                } while ((c -= 4) > 0);
+      }
+    }
+#else
+    for (c -= 1; c >= 0; c -= 1) {
+      b[c] = *pd++;
+    }
+#endif
+  }
+#else
+  int     x;
+  fp_int  t;
+
+  fp_init_copy(&t, a);
+
+  x = 0;
+  while (fp_iszero (&t) == FP_NO) {
+      b[x++] = (unsigned char) (t.dp[0] & 255);
+      fp_div_2d (&t, 8, &t, NULL);
+  }
+  fp_reverse (b, x);
+#endif
+}
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */