move the rescaling code into its own file and make enc/ and dec/ use it.

(cherry picked from commit 8e92d9e380a89b7443a2e2c3d16ce5a222e8c1e8)

Conflicts:

	Android.mk
	makefile.unix
	src/dec/vp8l.c
	src/utils/Makefile.am

Android.mk

@@ -39,6 +39,7 @@ LOCAL_SRC_FILES := \
 	src/utils/bit_writer.c \
 	src/utils/filters.c \
 	src/utils/quant_levels.c \
+	src/utils/rescaler.c \
 	src/utils/tcoder.c \
 	src/utils/thread.c \
 

Makefile.vc

@@ -188,6 +188,7 @@ X_OBJS= \
     $(DIROBJ)\utils\bit_writer.obj \
     $(DIROBJ)\utils\filters.obj \
     $(DIROBJ)\utils\quant_levels.obj \
+    $(DIROBJ)\utils\rescaler.obj \
     $(DIROBJ)\utils\tcoder.obj \
     $(DIROBJ)\utils\thread.obj \
     $(X_OBJS) \

makefile.unix

@@ -72,8 +72,8 @@ DSP_OBJS = src/dsp/cpu.o src/dsp/enc.o \
            src/dsp/dec_neon.o src/dsp/upsampling.o src/dsp/upsampling_sse2.o \
            src/dsp/yuv.o
 UTILS_OBJS = src/utils/alpha.o src/utils/bit_reader.o src/utils/bit_writer.o \
-             src/utils/filters.o src/utils/quant_levels.o src/utils/thread.o \
+             src/utils/filters.o src/utils/quant_levels.o src/utils/rescaler.o \
-             src/utils/tcoder.o
+             src/utils/thread.o src/utils/tcoder.o
 
 OBJS = $(DEC_OBJS) $(ENC_OBJS) $(DSP_OBJS) $(UTILS_OBJS)
 

src/dec/io.c

@@ -234,14 +234,11 @@ static int EmitAlphaRGBA4444(const VP8Io* const io, WebPDecParams* const p) {
 static int Rescale(const uint8_t* src, int src_stride,
                    int new_lines, WebPRescaler* const wrk) {
   int num_lines_out = 0;
-  while (new_lines-- > 0) {    // import new contribution of one source row.
+  while (new_lines > 0) {    // import new contributions of source rows.
-    WebPRescalerImportRow(src, 0, wrk);
+    const int lines_in = WebPRescalerImport(wrk, new_lines, src, src_stride);
-    src += src_stride;
+    src += lines_in * src_stride;
-    wrk->y_accum -= wrk->y_sub;
+    new_lines -= lines_in;
-    while (wrk->y_accum <= 0) {      // emit output row(s)
+    num_lines_out += WebPRescalerExport(wrk);    // emit output row(s)
-      WebPRescalerExportRow(wrk);
-      ++num_lines_out;
-    }
   }
   return num_lines_out;
 }
@@ -318,20 +315,6 @@ static int InitYUVRescaler(const VP8Io* const io, WebPDecParams* const p) {
 //------------------------------------------------------------------------------
 // RGBA rescaling
 
-// import new contributions until one row is ready to be output, or all input
-// is consumed.
-static int Import(const uint8_t* src, int src_stride,
-                  int new_lines, WebPRescaler* const wrk) {
-  int num_lines_in = 0;
-  while (num_lines_in < new_lines && wrk->y_accum > 0) {
-    WebPRescalerImportRow(src, 0, wrk);
-    src += src_stride;
-    ++num_lines_in;
-    wrk->y_accum -= wrk->y_sub;
-  }
-  return num_lines_in;
-}
-
 static int ExportRGB(WebPDecParams* const p, int y_pos) {
   const WebPYUV444Converter convert =
       WebPYUV444Converters[p->output->colorspace];
@@ -340,7 +323,8 @@ static int ExportRGB(WebPDecParams* const p, int y_pos) {
   int num_lines_out = 0;
   // For RGB rescaling, because of the YUV420, current scan position
   // U/V can be +1/-1 line from the Y one.  Hence the double test.
-  while (p->scaler_y.y_accum <= 0 && p->scaler_u.y_accum <= 0) {
+  while (WebPRescalerHasPendingOutput(&p->scaler_y) &&
+         WebPRescalerHasPendingOutput(&p->scaler_u)) {
     assert(p->last_y + y_pos + num_lines_out < p->output->height);
     assert(p->scaler_u.y_accum == p->scaler_v.y_accum);
     WebPRescalerExportRow(&p->scaler_y);
@@ -360,12 +344,15 @@ static int EmitRescaledRGB(const VP8Io* const io, WebPDecParams* const p) {
   int j = 0, uv_j = 0;
   int num_lines_out = 0;
   while (j < mb_h) {
-    const int y_lines_in = Import(io->y + j * io->y_stride, io->y_stride,
+    const int y_lines_in =
-                                  mb_h - j, &p->scaler_y);
+        WebPRescalerImport(&p->scaler_y, mb_h - j,
-    const int u_lines_in = Import(io->u + uv_j * io->uv_stride, io->uv_stride,
+                           io->y + j * io->y_stride, io->y_stride);
-                                  uv_mb_h - uv_j, &p->scaler_u);
+    const int u_lines_in =
-    const int v_lines_in = Import(io->v + uv_j * io->uv_stride, io->uv_stride,
+        WebPRescalerImport(&p->scaler_u, uv_mb_h - uv_j,
-                                  uv_mb_h - uv_j, &p->scaler_v);
+                           io->u + uv_j * io->uv_stride, io->uv_stride);
+    const int v_lines_in =
+        WebPRescalerImport(&p->scaler_v, uv_mb_h - uv_j,
+                           io->v + uv_j * io->uv_stride, io->uv_stride);
     (void)v_lines_in;   // remove a gcc warning
     assert(u_lines_in == v_lines_in);
     j += y_lines_in;
@@ -380,7 +367,7 @@ static int ExportAlpha(WebPDecParams* const p, int y_pos) {
   uint8_t* dst = buf->rgba + (p->last_y + y_pos) * buf->stride +
                  (p->output->colorspace == MODE_ARGB ? 0 : 3);
   int num_lines_out = 0;
-  while (p->scaler_a.y_accum <= 0) {
+  while (WebPRescalerHasPendingOutput(&p->scaler_a)) {
     int i;
     assert(p->last_y + y_pos + num_lines_out < p->output->height);
     WebPRescalerExportRow(&p->scaler_a);
@@ -397,7 +384,7 @@ static int ExportAlphaRGBA4444(WebPDecParams* const p, int y_pos) {
   const WebPRGBABuffer* const buf = &p->output->u.RGBA;
   uint8_t* dst = buf->rgba + (p->last_y + y_pos) * buf->stride + 1;
   int num_lines_out = 0;
-  while (p->scaler_a.y_accum <= 0) {
+  while (WebPRescalerHasPendingOutput(&p->scaler_a)) {
     int i;
     assert(p->last_y + y_pos + num_lines_out < p->output->height);
     WebPRescalerExportRow(&p->scaler_a);
@@ -420,7 +407,8 @@ static int EmitRescaledAlphaRGB(const VP8Io* const io, WebPDecParams* const p) {
     WebPRescaler* const scaler = &p->scaler_a;
     int j = 0, pos = 0;
     while (j < io->mb_h) {
-      j += Import(io->a + j * io->width, io->width, io->mb_h - j, scaler);
+      j += WebPRescalerImport(scaler, io->mb_h - j,
+                              io->a + j * io->width, io->width);
       pos += output_func(p, pos);
     }
   }

src/dec/webp.c

@@ -610,7 +610,7 @@ VP8StatusCode WebPDecode(const uint8_t* data, uint32_t data_size,
 }
 
 //------------------------------------------------------------------------------
-// Cropping & rescaling.
+// Cropping and rescaling.
 
 int WebPIoInitFromOptions(const WebPDecoderOptions* const options,
                           VP8Io* const io) {
@@ -664,97 +664,6 @@ int WebPIoInitFromOptions(const WebPDecoderOptions* const options,
   return 1;
 }
 
-#define RFIX 30
-#define MULT_FIX(x,y) (((int64_t)(x) * (y) + (1 << (RFIX - 1))) >> RFIX)
-
-void WebPRescalerInit(WebPRescaler* const wrk, int src_width, int src_height,
-                      uint8_t* const dst, int dst_width, int dst_height,
-                      int dst_stride, int num_channels, int x_add, int x_sub,
-                      int y_add, int y_sub, int32_t* const work) {
-  wrk->x_expand = (src_width < dst_width);
-  wrk->src_width = src_width;
-  wrk->src_height = src_height;
-  wrk->dst_width = dst_width;
-  wrk->dst_height = dst_height;
-  wrk->dst = dst;
-  wrk->dst_stride = dst_stride;
-  wrk->num_channels = num_channels;
-  // for 'x_expand', we use bilinear interpolation
-  wrk->x_add = wrk->x_expand ? (x_sub - 1) : x_add - x_sub;
-  wrk->x_sub = wrk->x_expand ? (x_add - 1) : x_sub;
-  wrk->y_accum = y_add;
-  wrk->y_add = y_add;
-  wrk->y_sub = y_sub;
-  wrk->fx_scale = (1 << RFIX) / x_sub;
-  wrk->fy_scale = (1 << RFIX) / y_sub;
-  wrk->fxy_scale = wrk->x_expand ?
-      ((int64_t)dst_height << RFIX) / (x_sub * src_height) :
-      ((int64_t)dst_height << RFIX) / (x_add * src_height);
-  wrk->irow = work;
-  wrk->frow = work + num_channels * dst_width;
-}
-
-void WebPRescalerImportRow(const uint8_t* const src, int channel,
-                           WebPRescaler* const wrk) {
-  const int x_stride = wrk->num_channels;
-  const int x_out_max = wrk->dst_width * wrk->num_channels;
-  int x_in = channel;
-  int x_out;
-  int accum = 0;
-  if (!wrk->x_expand) {
-    int sum = 0;
-    for (x_out = channel; x_out < x_out_max; x_out += x_stride) {
-      accum += wrk->x_add;
-      for (; accum > 0; accum -= wrk->x_sub) {
-        sum += src[x_in];
-        x_in += x_stride;
-      }
-      {        // Emit next horizontal pixel.
-        const int32_t base = src[x_in];
-        const int32_t frac = base * (-accum);
-        x_in += x_stride;
-        wrk->frow[x_out] = (sum + base) * wrk->x_sub - frac;
-        // fresh fractional start for next pixel
-        sum = (int)MULT_FIX(frac, wrk->fx_scale);
-      }
-    }
-  } else {        // simple bilinear interpolation
-    int left = src[channel], right = src[channel];
-    for (x_out = channel; x_out < x_out_max; x_out += x_stride) {
-      if (accum < 0) {
-        left = right;
-        x_in += x_stride;
-        right = src[x_in];
-        accum += wrk->x_add;
-      }
-      wrk->frow[x_out] = right * wrk->x_add + (left - right) * accum;
-      accum -= wrk->x_sub;
-    }
-  }
-  // Accumulate the new row's contribution
-  for (x_out = channel; x_out < x_out_max; x_out += x_stride) {
-    wrk->irow[x_out] += wrk->frow[x_out];
-  }
-}
-
-void WebPRescalerExportRow(WebPRescaler* const wrk) {
-  int x_out;
-  const int yscale = wrk->fy_scale * (-wrk->y_accum);
-  const int x_out_max = wrk->dst_width * wrk->num_channels;
-  assert(wrk->y_accum <= 0);
-  for (x_out = 0; x_out < x_out_max; ++x_out) {
-    const int frac = (int)MULT_FIX(wrk->frow[x_out], yscale);
-    const int v = (int)MULT_FIX(wrk->irow[x_out] - frac, wrk->fxy_scale);
-    wrk->dst[x_out] = (!(v & ~0xff)) ? v : (v < 0) ? 0 : 255;
-    wrk->irow[x_out] = frac;   // new fractional start
-  }
-  wrk->y_accum += wrk->y_add;
-  wrk->dst += wrk->dst_stride;
-}
-
-#undef MULT_FIX
-#undef RFIX
-
 //------------------------------------------------------------------------------
 
 #if defined(__cplusplus) || defined(c_plusplus)

src/dec/webpi.h

@@ -17,6 +17,7 @@ extern "C" {
 #endif
 
 #include "../webp/decode_vp8.h"
+#include "../utils/rescaler.h"
 
 //------------------------------------------------------------------------------
 // WebPDecParams: Decoding output parameters. Transient internal object.
@@ -24,23 +25,6 @@ extern "C" {
 typedef struct WebPDecParams WebPDecParams;
 typedef int (*OutputFunc)(const VP8Io* const io, WebPDecParams* const p);
 
-// Structure use for on-the-fly rescaling
-typedef struct {
-  int x_expand;               // true if we're expanding in the x direction
-  int num_channels;           // bytes to jump between pixels
-  int fy_scale, fx_scale;     // fixed-point scaling factor
-  int64_t fxy_scale;          // ''
-  // we need hpel-precise add/sub increments, for the downsampled U/V planes.
-  int y_accum;                // vertical accumulator
-  int y_add, y_sub;           // vertical increments (add ~= src, sub ~= dst)
-  int x_add, x_sub;           // horizontal increments (add ~= src, sub ~= dst)
-  int src_width, src_height;  // source dimensions
-  int dst_width, dst_height;  // destination dimensions
-  uint8_t* dst;
-  int dst_stride;
-  int32_t* irow, *frow;       // work buffer
-} WebPRescaler;
-
 struct WebPDecParams {
   WebPDecBuffer* output;             // output buffer.
   uint8_t* tmp_y, *tmp_u, *tmp_v;    // cache for the fancy upsampler
@@ -167,20 +151,6 @@ void WebPGrabDecBuffer(WebPDecBuffer* const src, WebPDecBuffer* const dst);
 int WebPIoInitFromOptions(const WebPDecoderOptions* const options,
                           VP8Io* const io);
 
-// Initialize a rescaler given scratch area 'work' and dimensions of src & dst.
-void WebPRescalerInit(WebPRescaler* const wrk, int src_width, int src_height,
-                      uint8_t* const dst, int dst_width, int dst_height,
-                      int dst_stride, int num_channels, int x_add, int x_sub,
-                      int y_add, int y_sub, int32_t* const work);
-
-// Import a row of data and save its contribution in the rescaler.
-// 'channel' denotes the channel number to be imported.
-void WebPRescalerImportRow(const uint8_t* const src, int channel,
-                           WebPRescaler* const wrk);
-
-// Export a row from rescaler.
-void WebPRescalerExportRow(WebPRescaler* const wrk);
-
 //------------------------------------------------------------------------------
 
 #if defined(__cplusplus) || defined(c_plusplus)

src/enc/picture.c

@@ -14,6 +14,7 @@
 #include <math.h>
 
 #include "./vp8enci.h"
+#include "../utils/rescaler.h"
 
 #if defined(__cplusplus) || defined(c_plusplus)
 extern "C" {
@@ -224,89 +225,29 @@ int WebPPictureCrop(WebPPicture* const pic,
 //------------------------------------------------------------------------------
 // Simple picture rescaler
 
-#define RFIX 30
-#define MULT(x,y) (((int64_t)(x) * (y) + (1 << (RFIX - 1))) >> RFIX)
-static WEBP_INLINE void ImportRow(const uint8_t* src, int src_width,
-                                  int32_t* frow, int32_t* irow, int dst_width) {
-  const int x_expand = (src_width < dst_width);
-  const int fx_scale = (1 << RFIX) / dst_width;
-  int x_in = 0;
-  int x_out;
-  int x_accum = 0;
-  if (!x_expand) {
-    int sum = 0;
-    for (x_out = 0; x_out < dst_width; ++x_out) {
-      x_accum += src_width - dst_width;
-      for (; x_accum > 0; x_accum -= dst_width) {
-        sum += src[x_in++];
-      }
-      {        // Emit next horizontal pixel.
-        const int32_t base = src[x_in++];
-        const int32_t frac = base * (-x_accum);
-        frow[x_out] = (sum + base) * dst_width - frac;
-        sum = MULT(frac, fx_scale);    // fresh fractional start for next pixel
-      }
-    }
-  } else {        // simple bilinear interpolation
-    int left = src[0], right = src[0];
-    for (x_out = 0; x_out < dst_width; ++x_out) {
-      if (x_accum < 0) {
-        left = right;
-        right = src[++x_in];
-        x_accum += dst_width - 1;
-      }
-      frow[x_out] = right * (dst_width - 1) + (left - right) * x_accum;
-      x_accum -= src_width - 1;
-    }
-  }
-  // Accumulate the new row's contribution
-  for (x_out = 0; x_out < dst_width; ++x_out) {
-    irow[x_out] += frow[x_out];
-  }
-}
-
-static void ExportRow(int32_t* frow, int32_t* irow, uint8_t* dst, int dst_width,
-                      const int yscale, const int64_t fxy_scale) {
-  int x_out;
-  for (x_out = 0; x_out < dst_width; ++x_out) {
-    const int frac = MULT(frow[x_out], yscale);
-    const int v = (int)(MULT(irow[x_out] - frac, fxy_scale));
-    dst[x_out] = (!(v & ~0xff)) ? v : (v < 0) ? 0 : 255;
-    irow[x_out] = frac;   // new fractional start
-  }
-}
-
 static void RescalePlane(const uint8_t* src,
                          int src_width, int src_height, int src_stride,
                          uint8_t* dst,
                          int dst_width, int dst_height, int dst_stride,
                          int32_t* const work) {
-  const int x_expand = (src_width < dst_width);
+  WebPRescaler rescaler;
-  const int fy_scale = (1 << RFIX) / dst_height;
+  int y = 0;
-  const int64_t fxy_scale = x_expand ?
-      ((int64_t)dst_height << RFIX) / (dst_width * src_height) :
-      ((int64_t)dst_height << RFIX) / (src_width * src_height);
-  int y_accum = src_height;
-  int y;
-  int32_t* irow = work;              // integral contribution
-  int32_t* frow = work + dst_width;  // fractional contribution
 
+  WebPRescalerInit(&rescaler, src_width, src_height,
+                   dst, dst_width, dst_height, dst_stride,
+                   1,
+                   src_width, dst_width,
+                   src_height, dst_height,
+                   work);
   memset(work, 0, 2 * dst_width * sizeof(*work));
-  for (y = 0; y < src_height; ++y) {
+  while (y < src_height) {
-    // import new contribution of one source row.
+    const int num_lines_in =
-    ImportRow(src, src_width, frow, irow, dst_width);
+        WebPRescalerImport(&rescaler, src_height - y, src, src_stride);
-    src += src_stride;
+    y += num_lines_in;
-    // emit output row(s)
+    src += num_lines_in * src_stride;
-    y_accum -= dst_height;
+    WebPRescalerExport(&rescaler);
-    for (; y_accum <= 0; y_accum += src_height) {
-      const int yscale = fy_scale * (-y_accum);
-      ExportRow(frow, irow, dst, dst_width, yscale, fxy_scale);
-      dst += dst_stride;
-    }
   }
 }
-#undef MULT
-#undef RFIX
 
 int WebPPictureRescale(WebPPicture* const pic, int width, int height) {
   WebPPicture tmp;
@@ -332,7 +273,7 @@ int WebPPictureRescale(WebPPicture* const pic, int width, int height) {
   tmp.height = height;
   if (!WebPPictureAlloc(&tmp)) return 0;
 
-  work = (int32_t*)malloc(2 * width * sizeof(int32_t));
+  work = (int32_t*)malloc(2 * width * sizeof(*work));
   if (work == NULL) {
     WebPPictureFree(&tmp);
     return 0;

src/utils/Makefile.am

@@ -4,7 +4,7 @@ libwebputils_la_SOURCES = alpha.h alpha.c \
                           bit_reader.h bit_reader.c \
                           bit_writer.h bit_writer.c \
                           filters.h filters.c \
-                          quant_levels.c \
+                          quant_levels.c rescaler.c \
                           tcoder.h tcoderi.h tcoder.c \
                           thread.h thread.c
 libwebputilsinclude_HEADERS = ../webp/types.h

src/utils/rescaler.c

@@ -0,0 +1,152 @@
+// Copyright 2012 Google Inc. All Rights Reserved.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Rescaling functions
+//
+// Author: Skal (pascal.massimino@gmail.com)
+
+#include <assert.h>
+#include <stdlib.h>
+#include "./rescaler.h"
+
+//------------------------------------------------------------------------------
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+#define RFIX 30
+#define MULT_FIX(x,y) (((int64_t)(x) * (y) + (1 << (RFIX - 1))) >> RFIX)
+
+void WebPRescalerInit(WebPRescaler* const wrk, int src_width, int src_height,
+                      uint8_t* const dst, int dst_width, int dst_height,
+                      int dst_stride, int num_channels, int x_add, int x_sub,
+                      int y_add, int y_sub, int32_t* const work) {
+  wrk->x_expand = (src_width < dst_width);
+  wrk->src_width = src_width;
+  wrk->src_height = src_height;
+  wrk->dst_width = dst_width;
+  wrk->dst_height = dst_height;
+  wrk->dst = dst;
+  wrk->dst_stride = dst_stride;
+  wrk->num_channels = num_channels;
+  // for 'x_expand', we use bilinear interpolation
+  wrk->x_add = wrk->x_expand ? (x_sub - 1) : x_add - x_sub;
+  wrk->x_sub = wrk->x_expand ? (x_add - 1) : x_sub;
+  wrk->y_accum = y_add;
+  wrk->y_add = y_add;
+  wrk->y_sub = y_sub;
+  wrk->fx_scale = (1 << RFIX) / x_sub;
+  wrk->fy_scale = (1 << RFIX) / y_sub;
+  wrk->fxy_scale = wrk->x_expand ?
+      ((int64_t)dst_height << RFIX) / (x_sub * src_height) :
+      ((int64_t)dst_height << RFIX) / (x_add * src_height);
+  wrk->irow = work;
+  wrk->frow = work + num_channels * dst_width;
+}
+
+void WebPRescalerImportRow(WebPRescaler* const wrk,
+                           const uint8_t* const src, int channel) {
+  const int x_stride = wrk->num_channels;
+  const int x_out_max = wrk->dst_width * wrk->num_channels;
+  int x_in = channel;
+  int x_out;
+  int accum = 0;
+  if (!wrk->x_expand) {
+    int sum = 0;
+    for (x_out = channel; x_out < x_out_max; x_out += x_stride) {
+      accum += wrk->x_add;
+      for (; accum > 0; accum -= wrk->x_sub) {
+        sum += src[x_in];
+        x_in += x_stride;
+      }
+      {        // Emit next horizontal pixel.
+        const int32_t base = src[x_in];
+        const int32_t frac = base * (-accum);
+        x_in += x_stride;
+        wrk->frow[x_out] = (sum + base) * wrk->x_sub - frac;
+        // fresh fractional start for next pixel
+        sum = (int)MULT_FIX(frac, wrk->fx_scale);
+      }
+    }
+  } else {        // simple bilinear interpolation
+    int left = src[channel], right = src[channel];
+    for (x_out = channel; x_out < x_out_max; x_out += x_stride) {
+      if (accum < 0) {
+        left = right;
+        x_in += x_stride;
+        right = src[x_in];
+        accum += wrk->x_add;
+      }
+      wrk->frow[x_out] = right * wrk->x_add + (left - right) * accum;
+      accum -= wrk->x_sub;
+    }
+  }
+  // Accumulate the new row's contribution
+  for (x_out = channel; x_out < x_out_max; x_out += x_stride) {
+    wrk->irow[x_out] += wrk->frow[x_out];
+  }
+}
+
+uint8_t* WebPRescalerExportRow(WebPRescaler* const wrk) {
+  if (wrk->y_accum <= 0) {
+    int x_out;
+    uint8_t* const dst = wrk->dst;
+    int32_t* const irow = wrk->irow;
+    const int32_t* const frow = wrk->frow;
+    const int yscale = wrk->fy_scale * (-wrk->y_accum);
+    const int x_out_max = wrk->dst_width * wrk->num_channels;
+
+    for (x_out = 0; x_out < x_out_max; ++x_out) {
+      const int frac = (int)MULT_FIX(frow[x_out], yscale);
+      const int v = (int)MULT_FIX(irow[x_out] - frac, wrk->fxy_scale);
+      dst[x_out] = (!(v & ~0xff)) ? v : (v < 0) ? 0 : 255;
+      irow[x_out] = frac;   // new fractional start
+    }
+    wrk->y_accum += wrk->y_add;
+    wrk->dst += wrk->dst_stride;
+    return dst;
+  } else {
+    return NULL;
+  }
+}
+
+#undef MULT_FIX
+#undef RFIX
+
+//------------------------------------------------------------------------------
+// all-in-one calls
+
+int WebPRescalerImport(WebPRescaler* const wrk, int num_lines,
+                       const uint8_t* src, int src_stride) {
+  int total_imported = 0;
+  while (total_imported < num_lines && wrk->y_accum > 0) {
+    int channel;
+    for (channel = 0; channel < wrk->num_channels; ++channel) {
+      WebPRescalerImportRow(wrk, src, channel);
+    }
+    src += src_stride;
+    ++total_imported;
+    wrk->y_accum -= wrk->y_sub;
+  }
+  return total_imported;
+}
+
+int WebPRescalerExport(WebPRescaler* const rescaler) {
+  int total_exported = 0;
+  while (WebPRescalerHasPendingOutput(rescaler)) {
+    WebPRescalerExportRow(rescaler);
+    ++total_exported;
+  }
+  return total_exported;
+}
+
+//------------------------------------------------------------------------------
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    // extern "C"
+#endif

src/utils/rescaler.h

@@ -0,0 +1,76 @@
+// Copyright 2012 Google Inc. All Rights Reserved.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Rescaling functions
+//
+// Author: skal@google.com (Pascal Massimino)
+
+#ifndef WEBP_UTILS_RESCALER_H_
+#define WEBP_UTILS_RESCALER_H_
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+#include "../webp/types.h"
+
+// Structure used for on-the-fly rescaling
+typedef struct {
+  int x_expand;               // true if we're expanding in the x direction
+  int num_channels;           // bytes to jump between pixels
+  int fy_scale, fx_scale;     // fixed-point scaling factor
+  int64_t fxy_scale;          // ''
+  // we need hpel-precise add/sub increments, for the downsampled U/V planes.
+  int y_accum;                // vertical accumulator
+  int y_add, y_sub;           // vertical increments (add ~= src, sub ~= dst)
+  int x_add, x_sub;           // horizontal increments (add ~= src, sub ~= dst)
+  int src_width, src_height;  // source dimensions
+  int dst_width, dst_height;  // destination dimensions
+  uint8_t* dst;
+  int dst_stride;
+  int32_t* irow, *frow;       // work buffer
+} WebPRescaler;
+
+// Initialize a rescaler given scratch area 'work' and dimensions of src & dst.
+void WebPRescalerInit(WebPRescaler* const wrk, int src_width, int src_height,
+                      uint8_t* const dst,
+                      int dst_width, int dst_height, int dst_stride,
+                      int num_channels,
+                      int x_add, int x_sub,
+                      int y_add, int y_sub,
+                      int32_t* const work);
+
+// Import a row of data and save its contribution in the rescaler.
+// 'channel' denotes the channel number to be imported.
+void WebPRescalerImportRow(WebPRescaler* const rescaler,
+                           const uint8_t* const src, int channel);
+
+// Import multiple rows over all channels, until at least one row is ready to
+// be exported. Returns the actual number of lines that were imported.
+int WebPRescalerImport(WebPRescaler* const rescaler, int num_rows,
+                       const uint8_t* src, int src_stride);
+
+// Return true if there is pending output rows ready.
+static WEBP_INLINE
+int WebPRescalerHasPendingOutput(const WebPRescaler* const rescaler) {
+  return (rescaler->y_accum <= 0);
+}
+
+// Export one row from rescaler. Returns the pointer where output was written,
+// or NULL if no row was pending.
+uint8_t* WebPRescalerExportRow(WebPRescaler* const wrk);
+
+// Export as many rows as possible. Return the numbers of rows written.
+int WebPRescalerExport(WebPRescaler* const wrk);
+
+//------------------------------------------------------------------------------
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    // extern "C"
+#endif
+
+#endif  /* WEBP_UTILS_RESCALER_H_ */