Optimize O(U)StringBuffer's append/insert taking float/double

rtl_(u)str_valueOf(Float/Double) are the most inefficient choice:
their implementations call rtl_math_doubleTo(U)String, asking to
allocate a new rtl_(u)String; then copy the string to the provided
buffer on stack, and destroy the rtl_(u)String; and then copy the
buffer into self. Even using O(U)String::number() would be more
efficient, avoiding the intermediate stack buffer copy.

But rtl_math_doubleTo(U)String can take also the O(U)StringBuffer's
data directly, allowing to insert efficiently. Use that.

Change-Id: I720ea7be6f4b2b92865a18eafcdb9ca9a089b854
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/151377
Tested-by: Mike Kaganski <mike.kaganski@collabora.com>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

2 files changed, 24 insertions, 16 deletions

diff --git a/include/rtl/strbuf.hxx b/include/rtl/strbuf.hxx
index e5ae1ebd0a7b..cb842bb5839e 100644
--- a/include/rtl/strbuf.hxx
+++ b/include/rtl/strbuf.hxx
@@ -756,8 +756,7 @@ public:
      */
     OStringBuffer & append(float f)
     {
-        char sz[RTL_STR_MAX_VALUEOFFLOAT];
-        return append( sz, rtl_str_valueOfFloat( sz, f ) );
+        return insert(getLength(), f);
     }
 
     /**
@@ -773,8 +772,7 @@ public:
      */
     OStringBuffer & append(double d)
     {
-        char sz[RTL_STR_MAX_VALUEOFDOUBLE];
-        return append( sz, rtl_str_valueOfDouble( sz, d ) );
+        return insert(getLength(), d);
     }
 
     /**
@@ -1032,8 +1030,11 @@ public:
      */
     OStringBuffer & insert(sal_Int32 offset, float f)
     {
-        char sz[RTL_STR_MAX_VALUEOFFLOAT];
-        return insert( offset, sz, rtl_str_valueOfFloat( sz, f ) );
+        // Same as rtl::str::valueOfFP, used for rtl_str_valueOfFloat
+        rtl_math_doubleToString(&pData, &nCapacity, offset, f, rtl_math_StringFormat_G,
+                                RTL_STR_MAX_VALUEOFFLOAT - SAL_N_ELEMENTS("-x.E-xxx") + 1, '.',
+                                NULL, 0, true);
+        return *this;
     }
 
     /**
@@ -1055,8 +1056,11 @@ public:
      */
     OStringBuffer & insert(sal_Int32 offset, double d)
     {
-        char sz[RTL_STR_MAX_VALUEOFDOUBLE];
-        return insert( offset, sz, rtl_str_valueOfDouble( sz, d ) );
+        // Same as rtl::str::valueOfFP, used for rtl_str_valueOfDouble
+        rtl_math_doubleToString(&pData, &nCapacity, offset, d, rtl_math_StringFormat_G,
+                                RTL_STR_MAX_VALUEOFDOUBLE - SAL_N_ELEMENTS("-x.E-xxx") + 1, '.',
+                                NULL, 0, true);
+        return *this;
     }
 
     /**
diff --git a/include/rtl/ustrbuf.hxx b/include/rtl/ustrbuf.hxx
index 363b4f24757f..227eed842443 100644
--- a/include/rtl/ustrbuf.hxx
+++ b/include/rtl/ustrbuf.hxx
@@ -916,8 +916,7 @@ public:
      */
     OUStringBuffer & append(float f)
     {
-        sal_Unicode sz[RTL_USTR_MAX_VALUEOFFLOAT];
-        return append( sz, rtl_ustr_valueOfFloat( sz, f ) );
+        return insert(getLength(), f);
     }
 
     /**
@@ -933,8 +932,7 @@ public:
      */
     OUStringBuffer & append(double d)
     {
-        sal_Unicode sz[RTL_USTR_MAX_VALUEOFDOUBLE];
-        return append( sz, rtl_ustr_valueOfDouble( sz, d ) );
+        return insert(getLength(), d);
     }
 
     /**
@@ -1288,8 +1286,11 @@ public:
      */
     OUStringBuffer & insert(sal_Int32 offset, float f)
     {
-        sal_Unicode sz[RTL_USTR_MAX_VALUEOFFLOAT];
-        return insert( offset, sz, rtl_ustr_valueOfFloat( sz, f ) );
+        // Same as rtl::str::valueOfFP, used for rtl_ustr_valueOfFloat
+        rtl_math_doubleToUString(&pData, &nCapacity, offset, f, rtl_math_StringFormat_G,
+                                 RTL_USTR_MAX_VALUEOFFLOAT - SAL_N_ELEMENTS("-x.E-xxx") + 1, '.',
+                                 NULL, 0, true);
+        return *this;
     }
 
     /**
@@ -1312,8 +1313,11 @@ public:
      */
     OUStringBuffer & insert(sal_Int32 offset, double d)
     {
-        sal_Unicode sz[RTL_USTR_MAX_VALUEOFDOUBLE];
-        return insert( offset, sz, rtl_ustr_valueOfDouble( sz, d ) );
+        // Same as rtl::str::valueOfFP, used for rtl_ustr_valueOfDouble
+        rtl_math_doubleToUString(&pData, &nCapacity, offset, d, rtl_math_StringFormat_G,
+                                 RTL_USTR_MAX_VALUEOFDOUBLE - SAL_N_ELEMENTS("-x.E-xxx") + 1, '.',
+                                 NULL, 0, true);
+        return *this;
     }
 
     /**