/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "ImageScaling.h"

#include "mozilla/Attributes.h"

#include "SSEHelpers.h"

/* The functions below use the following system for averaging 4 pixels:

 *

 * The first observation is that a half-adder is implemented as follows:

 * R = S + 2C or in the case of a and b (a ^ b) + ((a & b) << 1);

 *

 * This can be trivially extended to three pixels by observaring that when

 * doing (a ^ b ^ c) as the sum, the carry is simply the bitwise-or of the

 * carries of the individual numbers, since the sum of 3 bits can only ever

 * have a carry of one.

 *

 * We then observe that the average is then ((carry << 1) + sum) >> 1, or,

 * assuming eliminating overflows and underflows, carry + (sum >> 1).

 *

 * We now average our existing sum with the fourth number, so we get:

 * sum2 = (sum + d) >> 1 or (sum >> 1) + (d >> 1).

 *

 * We now observe that our sum has been moved into place relative to the

 * carry, so we can now average with the carry to get the final 4 input

 * average: avg = (sum2 + carry) >> 1;

 *

 * Or to reverse the proof:

 * avg = ((sum >> 1) + carry + d >> 1) >> 1

 * avg = ((a + b + c) >> 1 + d >> 1) >> 1

 * avg = ((a + b + c + d) >> 2)

 *

 * An additional fact used in the SSE versions is the concept that we can

 * trivially convert a rounded average to a truncated average:

 *

 * We have:

 * f(a, b) = (a + b + 1) >> 1

 *

 * And want:

 * g(a, b) = (a + b) >> 1

 *

 * Observe:

 * ~f(~a, ~b) == ~((~a + ~b + 1) >> 1)

 *            == ~((-a - 1 + -b - 1 + 1) >> 1)

 *            == ~((-a - 1 + -b) >> 1)

 *            == ~((-(a + b) - 1) >> 1)

 *            == ~((~(a + b)) >> 1)

 *            == (a + b) >> 1

 *            == g(a, b)

 */

MOZ_ALWAYS_INLINE __m128i _mm_not_si128(__m128i arg)

{

  __m128i minusone = _mm_set1_epi32(0xffffffff);

  return _mm_xor_si128(arg, minusone);

}

/* We have to pass pointers here, MSVC does not allow passing more than 3

 * __m128i arguments on the stack. And it does not allow 16-byte aligned

 * stack variables. This inlines properly on MSVC 2010. It does -not- inline

 * with just the inline directive.

 */

MOZ_ALWAYS_INLINE __m128i avg_sse2_8x2(__m128i *a, __m128i *b, __m128i *c, __m128i *d)

{

#define shuf1 _MM_SHUFFLE(2, 0, 2, 0)

#define shuf2 _MM_SHUFFLE(3, 1, 3, 1)

// This cannot be an inline function as the __Imm argument to _mm_shuffle_ps

// needs to be a compile time constant.

#define shuffle_si128(arga, argb, imm) \

  _mm_castps_si128(_mm_shuffle_ps(_mm_castsi128_ps((arga)), _mm_castsi128_ps((argb)), (imm)));

  __m128i t = shuffle_si128(*a, *b, shuf1);

  *b = shuffle_si128(*a, *b, shuf2);

  *a = t;

  t = shuffle_si128(*c, *d, shuf1);

  *d = shuffle_si128(*c, *d, shuf2);

  *c = t;

#undef shuf1

#undef shuf2

#undef shuffle_si128

  __m128i sum = _mm_xor_si128(*a, _mm_xor_si128(*b, *c));

  __m128i carry = _mm_or_si128(_mm_and_si128(*a, *b), _mm_or_si128(_mm_and_si128(*a, *c), _mm_and_si128(*b, *c)));

  sum = _mm_avg_epu8(_mm_not_si128(sum), _mm_not_si128(*d));

  return _mm_not_si128(_mm_avg_epu8(sum, _mm_not_si128(carry)));

}

MOZ_ALWAYS_INLINE __m128i avg_sse2_4x2_4x1(__m128i a, __m128i b)

{

  return _mm_not_si128(_mm_avg_epu8(_mm_not_si128(a), _mm_not_si128(b)));

}

MOZ_ALWAYS_INLINE __m128i avg_sse2_8x1_4x1(__m128i a, __m128i b)

{

  __m128i t = _mm_castps_si128(_mm_shuffle_ps(_mm_castsi128_ps(a), _mm_castsi128_ps(b), _MM_SHUFFLE(3, 1, 3, 1)));

  b = _mm_castps_si128(_mm_shuffle_ps(_mm_castsi128_ps(a), _mm_castsi128_ps(b), _MM_SHUFFLE(2, 0, 2, 0)));

  a = t;

  return _mm_not_si128(_mm_avg_epu8(_mm_not_si128(a), _mm_not_si128(b)));

}

MOZ_ALWAYS_INLINE uint32_t Avg2x2(uint32_t a, uint32_t b, uint32_t c, uint32_t d)

{

  uint32_t sum = a ^ b ^ c;

  uint32_t carry = (a & b) | (a & c) | (b & c);

  uint32_t mask = 0xfefefefe;

  // Not having a byte based average instruction means we should mask to avoid

  // underflow.

  sum = (((sum ^ d) & mask) >> 1) + (sum & d);

  return (((sum ^ carry) & mask) >> 1) + (sum & carry);

}

// Simple 2 pixel average version of the function above.

MOZ_ALWAYS_INLINE uint32_t Avg2(uint32_t a, uint32_t b)

{

  uint32_t sum = a ^ b;

  uint32_t carry = (a & b);

  uint32_t mask = 0xfefefefe;

  return ((sum & mask) >> 1) + carry;

}

namespace mozilla {

namespace gfx {

void

ImageHalfScaler::HalfImage2D_SSE2(uint8_t *aSource, int32_t aSourceStride,

                                  const IntSize &aSourceSize, uint8_t *aDest,

                                  uint32_t aDestStride)

{

  const int Bpp = 4;

  for (int y = 0; y < aSourceSize.height; y += 2) {

    __m128i *storage = (__m128i*)(aDest + (y / 2) * aDestStride);

    int x = 0;

    // Run a loop depending on alignment.

    if (!(uintptr_t(aSource + (y * aSourceStride)) % 16) &&

        !(uintptr_t(aSource + ((y + 1) * aSourceStride)) % 16)) {

      for (; x < (aSourceSize.width - 7); x += 8) {

        __m128i *upperRow = (__m128i*)(aSource + (y * aSourceStride + x * Bpp));

        __m128i *lowerRow = (__m128i*)(aSource + ((y + 1) * aSourceStride + x * Bpp));

        __m128i a = _mm_load_si128(upperRow);

        __m128i b = _mm_load_si128(upperRow + 1);

        __m128i c = _mm_load_si128(lowerRow);

        __m128i d = _mm_load_si128(lowerRow + 1);

        *storage++ = avg_sse2_8x2(&a, &b, &c, &d);

      }

    } else if (!(uintptr_t(aSource + (y * aSourceStride)) % 16)) {

      for (; x < (aSourceSize.width - 7); x += 8) {

        __m128i *upperRow = (__m128i*)(aSource + (y * aSourceStride + x * Bpp));

        __m128i *lowerRow = (__m128i*)(aSource + ((y + 1) * aSourceStride + x * Bpp));

        __m128i a = _mm_load_si128(upperRow);

        __m128i b = _mm_load_si128(upperRow + 1);

        __m128i c = loadUnaligned128(lowerRow);

        __m128i d = loadUnaligned128(lowerRow + 1);

        *storage++ = avg_sse2_8x2(&a, &b, &c, &d);

      }

    } else if (!(uintptr_t(aSource + ((y + 1) * aSourceStride)) % 16)) {

      for (; x < (aSourceSize.width - 7); x += 8) {

        __m128i *upperRow = (__m128i*)(aSource + (y * aSourceStride + x * Bpp));

        __m128i *lowerRow = (__m128i*)(aSource + ((y + 1) * aSourceStride + x * Bpp));

        __m128i a = loadUnaligned128((__m128i*)upperRow);

        __m128i b = loadUnaligned128((__m128i*)upperRow + 1);

        __m128i c = _mm_load_si128((__m128i*)lowerRow);

        __m128i d = _mm_load_si128((__m128i*)lowerRow + 1);

        *storage++ = avg_sse2_8x2(&a, &b, &c, &d);

      }

    } else {

      for (; x < (aSourceSize.width - 7); x += 8) {

        __m128i *upperRow = (__m128i*)(aSource + (y * aSourceStride + x * Bpp));

        __m128i *lowerRow = (__m128i*)(aSource + ((y + 1) * aSourceStride + x * Bpp));

        __m128i a = loadUnaligned128(upperRow);

        __m128i b = loadUnaligned128(upperRow + 1);

        __m128i c = loadUnaligned128(lowerRow);

        __m128i d = loadUnaligned128(lowerRow + 1);

        *storage++ = avg_sse2_8x2(&a, &b, &c, &d);

      }

    }

    uint32_t *unalignedStorage = (uint32_t*)storage;

    // Take care of the final pixels, we know there's an even number of pixels

    // in the source rectangle. We use a 2x2 'simd' implementation for this.

    //

    // Potentially we only have to do this in the last row since overflowing 

    // 8 pixels in an earlier row would appear to be harmless as it doesn't

    // touch invalid memory. Even when reading and writing to the same surface.

    // in practice we only do this when doing an additional downscale pass, and

    // in this situation we have unused stride to write into harmlessly.

    // I do not believe the additional code complexity would be worth it though.

    for (; x < aSourceSize.width; x += 2) {

      uint8_t *upperRow = aSource + (y * aSourceStride + x * Bpp);

      uint8_t *lowerRow = aSource + ((y + 1) * aSourceStride + x * Bpp);

      *unalignedStorage++ = Avg2x2(*(uint32_t*)upperRow, *((uint32_t*)upperRow + 1),

                                   *(uint32_t*)lowerRow, *((uint32_t*)lowerRow + 1));

    }

  }

}

void

ImageHalfScaler::HalfImageVertical_SSE2(uint8_t *aSource, int32_t aSourceStride,

                                        const IntSize &aSourceSize, uint8_t *aDest,

                                        uint32_t aDestStride)

{

  for (int y = 0; y < aSourceSize.height; y += 2) {

    __m128i *storage = (__m128i*)(aDest + (y / 2) * aDestStride);

    int x = 0;

    // Run a loop depending on alignment.

    if (!(uintptr_t(aSource + (y * aSourceStride)) % 16) &&

        !(uintptr_t(aSource + ((y + 1) * aSourceStride)) % 16)) {

      for (; x < (aSourceSize.width - 3); x += 4) {

        uint8_t *upperRow = aSource + (y * aSourceStride + x * 4);

        uint8_t *lowerRow = aSource + ((y + 1) * aSourceStride + x * 4);

        __m128i a = _mm_load_si128((__m128i*)upperRow);

        __m128i b = _mm_load_si128((__m128i*)lowerRow);

        *storage++ = avg_sse2_4x2_4x1(a, b);

      }

    } else if (!(uintptr_t(aSource + (y * aSourceStride)) % 16)) {

      // This line doesn't align well.

      for (; x < (aSourceSize.width - 3); x += 4) {

        uint8_t *upperRow = aSource + (y * aSourceStride + x * 4);

        uint8_t *lowerRow = aSource + ((y + 1) * aSourceStride + x * 4);

        __m128i a = _mm_load_si128((__m128i*)upperRow);

        __m128i b = loadUnaligned128((__m128i*)lowerRow);

        *storage++ = avg_sse2_4x2_4x1(a, b);

      }

    } else if (!(uintptr_t(aSource + ((y + 1) * aSourceStride)) % 16)) {

      for (; x < (aSourceSize.width - 3); x += 4) {

        uint8_t *upperRow = aSource + (y * aSourceStride + x * 4);

        uint8_t *lowerRow = aSource + ((y + 1) * aSourceStride + x * 4);

        __m128i a = loadUnaligned128((__m128i*)upperRow);

        __m128i b = _mm_load_si128((__m128i*)lowerRow);

        *storage++ = avg_sse2_4x2_4x1(a, b);

      }

    } else {

      for (; x < (aSourceSize.width - 3); x += 4) {

        uint8_t *upperRow = aSource + (y * aSourceStride + x * 4);

        uint8_t *lowerRow = aSource + ((y + 1) * aSourceStride + x * 4);

        __m128i a = loadUnaligned128((__m128i*)upperRow);

        __m128i b = loadUnaligned128((__m128i*)lowerRow);

        *storage++ = avg_sse2_4x2_4x1(a, b);

      }

    }

    uint32_t *unalignedStorage = (uint32_t*)storage;

    // Take care of the final pixels, we know there's an even number of pixels

    // in the source rectangle.

    //

    // Similar overflow considerations are valid as in the previous function.

    for (; x < aSourceSize.width; x++) {

      uint8_t *upperRow = aSource + (y * aSourceStride + x * 4);

      uint8_t *lowerRow = aSource + ((y + 1) * aSourceStride + x * 4);

      *unalignedStorage++ = Avg2(*(uint32_t*)upperRow, *(uint32_t*)lowerRow);

    }

  }

}

void

ImageHalfScaler::HalfImageHorizontal_SSE2(uint8_t *aSource, int32_t aSourceStride,

                                          const IntSize &aSourceSize, uint8_t *aDest,

                                          uint32_t aDestStride)

{

  for (int y = 0; y < aSourceSize.height; y++) {

    __m128i *storage = (__m128i*)(aDest + (y * aDestStride));

    int x = 0;

    // Run a loop depending on alignment.

    if (!(uintptr_t(aSource + (y * aSourceStride)) % 16)) {

      for (; x < (aSourceSize.width - 7); x += 8) {

        __m128i* pixels = (__m128i*)(aSource + (y * aSourceStride + x * 4));

        __m128i a = _mm_load_si128(pixels);

        __m128i b = _mm_load_si128(pixels + 1);

        *storage++ = avg_sse2_8x1_4x1(a, b);

      }

    } else {

      for (; x < (aSourceSize.width - 7); x += 8) {

        __m128i* pixels = (__m128i*)(aSource + (y * aSourceStride + x * 4));

        __m128i a = loadUnaligned128(pixels);

        __m128i b = loadUnaligned128(pixels + 1);

        *storage++ = avg_sse2_8x1_4x1(a, b);

      }

    }

    uint32_t *unalignedStorage = (uint32_t*)storage;

    // Take care of the final pixels, we know there's an even number of pixels

    // in the source rectangle.

    //

    // Similar overflow considerations are valid as in the previous function.

    for (; x < aSourceSize.width; x += 2) {

      uint32_t *pixels = (uint32_t*)(aSource + (y * aSourceStride + x * 4));

      *unalignedStorage++ = Avg2(*pixels, *(pixels + 1));

    }

  }

}

} // namespace gfx

} // namespace mozilla