lerp-study.cpp File Reference

#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdint>
#include "experimental/lowp-basic/QMath.h"

Go to the source code of this file.

Classes
struct	Stats

Functions
static float	golden_lerp (float t, int16_t a, int16_t b)
template<int logPixelScale>
static int16_t	saturating_lerp (float t, int16_t a, int16_t b)
template<int logPixelScale>
static int16_t	ssse3_lerp (float t, int16_t a, int16_t b)
static int16_t	full_res_lerp (float t, int16_t a, int16_t b)
template<int logPixelScale>
static int16_t	balanced_lerp (float t, int16_t a, int16_t b)
template<typename Lerp >
static Stats	check_lerp (Lerp lerp)
int	main ()

Function Documentation

balanced_lerp()

template<int logPixelScale>

static int16_t balanced_lerp ( float  t, int16_t  a, int16_t  b  )

static

Definition at line 72 of file lerp-study.cpp.

                                                            {
    const int16_t half = 1 << logPixelScale;
    // t on [-1, 1).
    Q15 qt (floor(t * 65536.0f - 32768.0f + 0.5f));
    // need to pick logPixelScale to scale by addition 1/2.
    Q15 qw ((b - a) << logPixelScale);
    Q15 qm ((a + b) << logPixelScale);
    Q15 answer = simulate_ssse3_mm_mulhrs_epi16(qt, qw) + qm;
    // Extra shift to divide by 2.
    return (answer[0] + half) >> (logPixelScale + 1);
}

check_lerp()

template<typename Lerp >

static Stats check_lerp ( Lerp  lerp )

static

Definition at line 85 of file lerp-study.cpp.

                                   {
    Stats stats;
    for (float t = 0; t < 1.0f - 1.0f / 65536.0f ; t += 1.0f/65536.0f)
    for (int a = 255; a >= 0; a--)
    for (int b = 255; b >= 0; b--) {
        float l = golden_lerp(t, a, b);
        int16_t golden = floor(l + 0.5f);
        int16_t candidate = lerp(t, a, b);
        stats.log(golden, candidate);
    }
    return stats;
}

full_res_lerp()

static int16_t full_res_lerp ( float  t, int16_t  a, int16_t  b  )

static

Definition at line 62 of file lerp-study.cpp.

                                                            {
    int32_t ft(floor(t * 65536.0f + 0.5f));
 
    int32_t temp = ft * (b - a) + a * 65536;
    int32_t rounded = temp + 32768;
    return rounded >> 16;
}

golden_lerp()

static float golden_lerp ( float  t, int16_t  a, int16_t  b  )

static

Definition at line 36 of file lerp-study.cpp.

                                                        {
    return (1.0f - t) * a + t * b;
}

main()

int main

(

)

Definition at line 98 of file lerp-study.cpp.

           {
    Stats stats;
 
    printf("\nUsing full_res_lerp...\n");
    stats = check_lerp(full_res_lerp);
    stats.print();
 
    printf("\nUsing vqrdmulhq_s16...\n");
    stats = check_lerp(saturating_lerp<7>);
    stats.print();
 
    printf("\nUsing mm_mulhrs_epi16...\n");
    stats = check_lerp(ssse3_lerp<7>);
    stats.print();
 
    printf("\nInterval [-1, 1) mm_mulhrs_epi16...\n");
    stats = check_lerp(balanced_lerp<7>);
    stats.print();
 
    printf("Done.");
    return 0;
}

saturating_lerp()

template<int logPixelScale>

static int16_t saturating_lerp ( float  t, int16_t  a, int16_t  b  )

static

Definition at line 41 of file lerp-study.cpp.

                                                              {
    const int16_t half = 1 << (logPixelScale - 1);
    Q15 qt(floor(t * 32768.f + 0.5f));
    Q15 qa(a << logPixelScale);
    Q15 qb(b << logPixelScale);
 
    Q15 answer = simulate_neon_vqrdmulhq_s16(qt, qb - qa) + qa;
    return (answer[0] + half) >> logPixelScale;
}

ssse3_lerp()

template<int logPixelScale>

static int16_t ssse3_lerp ( float  t, int16_t  a, int16_t  b  )

static

Definition at line 52 of file lerp-study.cpp.

                                                         {
    const int16_t half = 1 << (logPixelScale - 1);
    Q15 qt(floor(t * 32768.f + 0.5f));
    Q15 qa(a << logPixelScale);
    Q15 qb(b << logPixelScale);
 
    Q15 answer = simulate_ssse3_mm_mulhrs_epi16(qt, qb - qa) + qa;
    return (answer[0] + half) >> logPixelScale;
}