From 580a2656d10cc7c1fc93e094d7eb71f04d99c329 Mon Sep 17 00:00:00 2001
From: Jim Mussared
Date: Wed, 9 Oct 2019 22:59:35 +1100
Subject: stm32: Use hardware double sqrt on F7/H7 MCUs.

Identical to cd527bb324ade952d11a134859d38bf5272c165e but for doubles.
This gives a -2.754% improvement on bm_float.py, and -35% improvement on
calling sqrt in a loop.
---
 lib/libm_dbl/thumb_vfp_sqrt.c | 10 ++++++++++
 1 file changed, 10 insertions(+)
 create mode 100644 lib/libm_dbl/thumb_vfp_sqrt.c

(limited to 'lib')

diff --git a/lib/libm_dbl/thumb_vfp_sqrt.c b/lib/libm_dbl/thumb_vfp_sqrt.c
new file mode 100644
index 000000000..dd37a07b0
--- /dev/null
+++ b/lib/libm_dbl/thumb_vfp_sqrt.c
@@ -0,0 +1,10 @@
+// an implementation of sqrt for Thumb using hardware double-precision VFP instructions
+
+double sqrt(double x) {
+    double ret;
+    asm volatile (
+            "vsqrt.f64  %P0, %P1\n"
+            : "=w" (ret)
+            : "w"  (x));
+    return ret;
+}
-- 
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