[Beignet] [PATCH] fix built-in function "length"

[Homer Hsing]

if vector is zero, then returns zero.
if vector is very large, then do a scaling first.

Signed-off-by: Homer Hsing <homer.xing at intel.com>
---
 backend/src/ocl_stdlib.tmpl.h | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/backend/src/ocl_stdlib.tmpl.h b/backend/src/ocl_stdlib.tmpl.h
index e6d7910..a3bf0a0 100644
--- a/backend/src/ocl_stdlib.tmpl.h
+++ b/backend/src/ocl_stdlib.tmpl.h
@@ -1740,9 +1740,28 @@ INLINE_OVERLOADABLE float dot(float4 p0, float4 p1) {
   return p0.x * p1.x + p0.y * p1.y + p0.z * p1.z + p0.w * p1.w;
 }
 INLINE_OVERLOADABLE float length(float x) { return __gen_ocl_fabs(x); }
-INLINE_OVERLOADABLE float length(float2 x) { return sqrt(dot(x,x)); }
-INLINE_OVERLOADABLE float length(float3 x) { return sqrt(dot(x,x)); }
-INLINE_OVERLOADABLE float length(float4 x) { return sqrt(dot(x,x)); }
+#define BODY \
+  if(m == 0) \
+    return 0; \
+  if(isinf(m)) \
+    return INFINITY; \
+  if(m < 1) \
+    m = 1; \
+  x /= m; \
+  return m * sqrt(dot(x,x));
+INLINE_OVERLOADABLE float length(float2 x) {
+  float m = max(__gen_ocl_fabs(x.s0), __gen_ocl_fabs(x.s1));
+  BODY;
+}
+INLINE_OVERLOADABLE float length(float3 x) {
+  float m = max(__gen_ocl_fabs(x.s0), max(__gen_ocl_fabs(x.s1), __gen_ocl_fabs(x.s2)));
+  BODY;
+}
+INLINE_OVERLOADABLE float length(float4 x) {
+  float m = max(__gen_ocl_fabs(x.s0), max(__gen_ocl_fabs(x.s1), max(__gen_ocl_fabs(x.s2), __gen_ocl_fabs(x.s3))));
+  BODY;
+}
+#undef BODY
 INLINE_OVERLOADABLE float distance(float x, float y) { return length(x-y); }
 INLINE_OVERLOADABLE float distance(float2 x, float2 y) { return length(x-y); }
 INLINE_OVERLOADABLE float distance(float3 x, float3 y) { return length(x-y); }
-- 
1.8.3.2