ICU-103 add getNextUChar() helper ucnv_getUChar32KeepOverflow()

X-SVN-Rev: 1914

icu4c/source/common/ucnv_cnv.c

@@ -115,3 +115,56 @@ void  flushInternalCharBuffer (UConverter * _this,
 
   return;
 }
+
+/**
+ * This function is useful for implementations of getNextUChar().
+ * After a call to a callback function or to toUnicode(), an output buffer
+ * begins with a Unicode code point that needs to be returned as UChar32,
+ * and all following code units must be prepended to the - potentially
+ * prefilled - overflow buffer in the UConverter.
+ * The buffer should be at least of capacity UTF_MAX_CHAR_LENGTH so that a
+ * complete UChar32's UChars fit into it.
+ *
+ * @param cnv    The converter that will get remaining UChars copied to its overflow area.
+ * @param buffer An array of UChars that was passed into a callback function
+ *               or a toUnicode() function.
+ * @param length The number of code units (UChars) that are actually in the buffer.
+ *               This must be >0.
+ * @return The code point from the first UChars in the buffer.
+ */
+U_CFUNC UChar32
+ucnv_getUChar32KeepOverflow(UConverter *cnv, const UChar *buffer, int32_t length) {
+    UChar32 c;
+    int32_t i;
+
+    if(length<=0) {
+        return 0xffff;
+    }
+
+    /* get the first code point in the buffer */
+    i=0;
+    UTF_NEXT_CHAR_SAFE(buffer, i, length, c, FALSE);
+    if(i<length) {
+        /* there are UChars left in the buffer that need to go into the overflow buffer */
+        UChar *overflow=cnv->UCharErrorBuffer;
+        int32_t j=cnv->UCharErrorBufferLength;
+
+        if(j>0) {
+            /* move the overflow buffer contents to make room for the extra UChars */
+            int32_t k;
+
+            cnv->UCharErrorBufferLength=(int8_t)(k=(length-i)+j);
+            do {
+                overflow[--k]=overflow[--j];
+            } while(j>0);
+        } else {
+            cnv->UCharErrorBufferLength=(int8_t)(length-i);
+        }
+
+        /* copy the remaining UChars to the beginning of the overflow buffer */
+        do {
+            overflow[j++]=buffer[i++];
+        } while(i<length);
+    }
+    return c;
+}

icu4c/source/common/ucnv_cnv.h

@@ -220,4 +220,23 @@ extern const UConverterSharedData
 
 U_CDECL_END
 
+/**
+ * This function is useful for implementations of getNextUChar().
+ * After a call to a callback function or to toUnicode(), an output buffer
+ * begins with a Unicode code point that needs to be returned as UChar32,
+ * and all following code units must be prepended to the - potentially
+ * prefilled - overflow buffer in the UConverter.
+ * The buffer should be at least of capacity UTF_MAX_CHAR_LENGTH so that a
+ * complete UChar32's UChars fit into it.
+ *
+ * @param cnv    The converter that will get remaining UChars copied to its overflow area.
+ * @param buffer An array of UChars that was passed into a callback function
+ *               or a toUnicode() function.
+ * @param length The number of code units (UChars) that are actually in the buffer.
+ *               This must be >0.
+ * @return The code point from the first UChars in the buffer.
+ */
+U_CFUNC UChar32
+ucnv_getUChar32KeepOverflow(UConverter *cnv, const UChar *buffer, int32_t length);
+
 #endif /* UCNV_CNV */