libpng: Optimize RGBA png_do_expand_palette

third_party/libpng/arm/arm_palette.c

+/* palette_neon_intrinsics.c - NEON optimised palette expansion functions
+ *
+ * Copyright (c) 2017 ARM Limited
+ * Copyright (c) 2017 Glenn Randers-Pehrson
+ * Written by Richard Townsend <Richard.Townsend@arm.com>, February 2017.
+ *
+ * This code is released under the libpng license.
+ * For conditions of distribution and use, see the disclaimer
+ * and license in png.h
+ */
+
+#include "../pngpriv.h"
+
+#if PNG_ARM_NEON_IMPLEMENTATION == 1
+
+#include <arm_neon.h>
+
+/* Build an RGBA palette from the RGB and separate alpha palettes. */
+void
+png_riffle_palette(png_structrp png_ptr, png_row_infop row_info)
+{
+   png_const_colorp palette = png_ptr->palette;
+   png_bytep riffled_palette = png_ptr->row_tmp_palette;
+   png_const_bytep trans_alpha = png_ptr->trans_alpha;
+   int num_trans = png_ptr->num_trans;
+
+   int i;
+   for (i = 0; i < (1 << row_info->bit_depth); i++) {
+      riffled_palette[(i << 2) + 0] = palette[i].red;
+      riffled_palette[(i << 2) + 1] = palette[i].green;
+      riffled_palette[(i << 2) + 2] = palette[i].blue;
+      if (i >= num_trans) {
+         riffled_palette[(i << 2) + 3] = 0xff;
+      } else {
+         riffled_palette[(i << 2) + 3] = trans_alpha[i];
+      }
+   }
+}
+
+/* Expands a palettized row into RGBA. */
+int
+png_do_expand_palette_neon(png_structrp png_ptr, png_row_infop row_info,
+   png_const_bytep row, const png_bytepp ssp, const png_bytepp ddp)
+{
+
+   png_uint_32 row_width = row_info->width;
+   const png_uint_32 *riffled_palette = (const png_uint_32*)png_ptr->row_tmp_palette;
+   int i;
+
+   if (row_width >= 4) {
+      /* This function originally gets the last byte of the output row
+         The NEON part writes forward from a given position, so we have
+         to seek this back by 4 pixels x 4 bytes, for a total offset of 16.
+         We should only update the output pointer if the loop's going to run.*/
+      *ddp = *ddp - 15;
+   }
+
+   for(i = 0; i < row_width; i += 4) {
+      uint32x4_t cur;
+      png_bytep sp = *ssp - i, dp = *ddp - (i << 2);
+      cur = vld1q_dup_u32 (riffled_palette + *(sp - 3));
+      cur = vld1q_lane_u32(riffled_palette + *(sp - 2), cur, 1);
+      cur = vld1q_lane_u32(riffled_palette + *(sp - 1), cur, 2);
+      cur = vld1q_lane_u32(riffled_palette + *(sp), cur, 3);
+      vst1q_u32((void *)dp, cur);
+   }
+   if (i != row_width) {
+      i -= 4; /* Remove the amount that wasn't processed */
+   }
+
+   /* Decrement output pointers. */
+   *ssp = *ssp - i;
+   *ddp = *ddp - (i << 2);
+   return i;
+}
+
+#endif /* PNG_ARM_NEON_IMPLEMENTATION */