From: "Tomas Härdin" <git@haerdin.se>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 2/2] avcodec/jpeg2000dec: Add support for HTJ2K decoding.
Date: Fri, 02 Dec 2022 19:46:19 +0100
Message-ID: <6e60f8996f0d4d47cd988b99d7fe6b12d6e92846.camel@haerdin.se> (raw)
In-Reply-To: <20221202181130.87107-1-etemesicaleb@gmail.com>
fre 2022-12-02 klockan 21:11 +0300 skrev etemesicaleb@gmail.com:
>
> +/**
> + * Given a precomputed c, checks whether n % d == 0
> + */
> +static av_always_inline uint32_t is_divisible(uint32_t n, uint64_t
> c)
> +{
> + return n * c <= c - 1;
> +}
This looks like something that could go in lavu, say intmath.h
> +
> +/**
> + * @brief Refill the buffer backwards in little Endian while
> skipping
> + * over stuffing bits
> + *
> + * Stuffing bits are those that appear in the position of any byte
> whose
> + * LSBs are all 1's if the last consumed byte was larger than 0x8F
> + */
> +static int jpeg2000_bitbuf_refill_backwards(StateVars *buffer,
> + const uint8_t *array)
Don't we already have sufficient bitreading capabilities already? Maybe
it doesn't do the necessary unstuffing..
> + /*
> + * As an optimization, we can replace modulo operations with
> + * checking if a number is divisible , since that's the only
> thing we need.
> + * this is paired with is_divisible.
> + * Credits to Daniel Lemire blog post:
> + *
> https://lemire.me/blog/2019/02/08/faster-remainders-when-the-divisor-is-a-constant-beating-compilers-and-libdivide/
> + * It's UB on zero, but we can't have a quad being zero, the
> spec doesn't allow,
> + * so we error out early in case that's the case.
> + */
> +
> + c = 1 + UINT64_C(0xffffffffffffffff) / quad_width;
Just 0xffffffffffffffffULL would work
> +
> + for (int row = 1; row < quad_height; row++) {
> + while ((q - (row * quad_width)) < quad_width - 1 && q <
> (quad_height * quad_width)) {
> + q1 = q;
> + q2 = q + 1;
> + context1 = sigma_n[4 * (q1 - quad_width) + 1];
> + context1 += sigma_n[4 * (q1 - quad_width) + 3] << 2; //
> ne
> +
> + if (!is_divisible(q1, c)) {
These divisibility checks look like they could be even simpler given
that q always increases by 2
> + context1 |= sigma_n[4 * (q1 - quad_width) -
> 1]; // nw
> + context1 += (sigma_n[4 * q1 - 1] | sigma_n[4 * q1 -
> 2]) << 1; // sw| q
> + }
> + if (!is_divisible(q1 + 1, c))
> + context1 |= sigma_n[4 * (q1 - quad_width) + 5] << 2;
> +
> + if ((ret = jpeg2000_decode_sig_emb(s, mel_state,
> mel_stream, vlc_stream,
> + dec_CxtVLC_table1,
> Dcup, sig_pat, res_off,
> + emb_pat_k, emb_pat_1,
> J2K_Q1, context1, Lcup,
> + Pcup))
> + < 0)
> + goto free;
> +
> + for (int i = 0; i < 4; i++)
> + sigma_n[4 * q1 + i] = (sig_pat[J2K_Q1] >> i) & 1;
> +
> + context2 = sigma_n[4 * (q2 - quad_width) + 1];
> + context2 += sigma_n[4 * (q2 - quad_width) + 3] << 2;
> +
> + if (!is_divisible(q2, c)) {
> + context2 |= sigma_n[4 * (q2 - quad_width) - 1];
> + context2 += (sigma_n[4 * q2 - 1] | sigma_n[4 * q2 -
> 2]) << 1;
> + }
> + if (!is_divisible(q2 + 1, c))
> + context2 |= sigma_n[4 * (q2 - quad_width) + 5] << 2;
> +
> + if ((ret = jpeg2000_decode_sig_emb(s, mel_state,
> mel_stream, vlc_stream,
> + dec_CxtVLC_table1,
> Dcup, sig_pat, res_off,
> + emb_pat_k, emb_pat_1,
> J2K_Q2, context2, Lcup,
> + Pcup))
> + < 0)
> + goto free;
> +
> + for (int i = 0; i < 4; i++)
> + sigma_n[4 * q2 + i] = (sig_pat[J2K_Q2] >> i) & 1;
> +
> + u[J2K_Q1] = 0;
> + u[J2K_Q2] = 0;
> +
> + jpeg2000_bitbuf_refill_backwards(vlc_stream, vlc_buf);
> +
> + if (res_off[J2K_Q1] == 1 && res_off[J2K_Q2] == 1) {
> + u_pfx[J2K_Q1] = vlc_decode_u_prefix(vlc_stream,
> vlc_buf);
> + u_pfx[J2K_Q2] = vlc_decode_u_prefix(vlc_stream,
> vlc_buf);
> +
> + u_sfx[J2K_Q1] = vlc_decode_u_suffix(vlc_stream,
> u_pfx[J2K_Q1], vlc_buf);
> + u_sfx[J2K_Q2] = vlc_decode_u_suffix(vlc_stream,
> u_pfx[J2K_Q2], vlc_buf);
> +
> + u_ext[J2K_Q1] = vlc_decode_u_extension(vlc_stream,
> u_sfx[J2K_Q1], vlc_buf);
> + u_ext[J2K_Q2] = vlc_decode_u_extension(vlc_stream,
> u_sfx[J2K_Q2], vlc_buf);
> +
> + u[J2K_Q1] = u_pfx[J2K_Q1] + u_sfx[J2K_Q1] +
> (u_ext[J2K_Q1] << 2);
> + u[J2K_Q2] = u_pfx[J2K_Q2] + u_sfx[J2K_Q2] +
> (u_ext[J2K_Q2] << 2);
> +
> + } else if (res_off[J2K_Q1] == 1 || res_off[J2K_Q2] == 1)
> {
> + uint8_t pos = res_off[J2K_Q1] == 1 ? 0 : 1;
> +
> + u_pfx[pos] = vlc_decode_u_prefix(vlc_stream,
> vlc_buf);
> + u_sfx[pos] = vlc_decode_u_suffix(vlc_stream,
> u_pfx[pos], vlc_buf);
> + u_ext[pos] = vlc_decode_u_extension(vlc_stream,
> u_sfx[pos], vlc_buf);
> +
> + u[pos] = u_pfx[pos] + u_sfx[pos] + (u_ext[pos] <<
> 2);
> + }
> + sp = sig_pat[J2K_Q1];
> +
> + gamma[J2K_Q1] = 1;
> +
> + if (sp == 0 || sp == 1 || sp == 2 || sp == 4 || sp == 8)
> + gamma[J2K_Q1] = 0;
> +
> + sp = sig_pat[J2K_Q2];
> +
> + gamma[J2K_Q2] = 1;
> +
> + if (sp == 0 || sp == 1 || sp == 2 || sp == 4 || sp == 8)
> + gamma[J2K_Q2] = 0;
> +
> + E_n[J2K_Q1] = E[4 * (q1 - quad_width) + 1];
> + E_n[J2K_Q2] = E[4 * (q2 - quad_width) + 1];
> +
> + E_ne[J2K_Q1] = E[4 * (q1 - quad_width) + 3];
> + E_ne[J2K_Q2] = E[4 * (q2 - quad_width) + 3];
> +
> + E_nw[J2K_Q1] = (!is_divisible(q1, c)) * E[FFMAX((4 * (q1
> - quad_width) - 1), 0)];
> + E_nw[J2K_Q2] = (!is_divisible(q2, c)) * E[FFMAX((4 * (q2
> - quad_width) - 1), 0)];
> +
> + E_nf[J2K_Q1] = (!is_divisible(q1 + 1, c)) * E[4 * (q1 -
> quad_width) + 5];
> + E_nf[J2K_Q2] = (!is_divisible(q2 + 1, c)) * E[4 * (q2 -
> quad_width) + 5];
> +
> + max_e[J2K_Q1] = FFMAX(E_nw[J2K_Q1], FFMAX3(E_n[J2K_Q1],
> E_ne[J2K_Q1], E_nf[J2K_Q1]));
> + max_e[J2K_Q2] = FFMAX(E_nw[J2K_Q2], FFMAX3(E_n[J2K_Q2],
> E_ne[J2K_Q2], E_nf[J2K_Q2]));
> +
> + kappa[J2K_Q1] = FFMAX(1, gamma[J2K_Q1] * (max_e[J2K_Q1]
> - 1));
> + kappa[J2K_Q2] = FFMAX(1, gamma[J2K_Q2] * (max_e[J2K_Q2]
> - 1));
> +
> + U[J2K_Q1] = kappa[J2K_Q1] + u[J2K_Q1];
> + U[J2K_Q2] = kappa[J2K_Q2] + u[J2K_Q2];
> +
> + for (int i = 0; i < 4; i++) {
> + m[J2K_Q1][i] = sigma_n[4 * q1 + i] * U[J2K_Q1] -
> ((emb_pat_k[J2K_Q1] >> i) & 1);
> + m[J2K_Q2][i] = sigma_n[4 * q2 + i] * U[J2K_Q2] -
> ((emb_pat_k[J2K_Q2] >> i) & 1);
> + }
> + recover_mag_sgn(mag_sgn_stream, J2K_Q1, q1, m_n,
> known_1, emb_pat_1, v, m,
> + E, mu_n, Dcup, Pcup, pLSB);
> +
> + recover_mag_sgn(mag_sgn_stream, J2K_Q2, q2, m_n,
> known_1, emb_pat_1, v, m,
> + E, mu_n, Dcup, Pcup, pLSB);
> +
> + /* move to the next quad pair */
> + q += 2;
> + }
> + if (quad_width % 2 == 1) {
> + q1 = q;
> + /* calculate context for current quad */
> + context1 = sigma_n[4 * (q1 - quad_width) + 1];
> + context1 += (sigma_n[4 * (q1 - quad_width) + 3] << 2);
> +
> + if (!is_divisible(q1, c)) {
> + context1 |= sigma_n[4 * (q1 - quad_width) - 1];
> + context1 += (sigma_n[4 * q1 - 1] | sigma_n[4 * q1 -
> 2]) << 1;
> + }
> + if (!is_divisible(q1 + 1, c))
> + context1 |= sigma_n[4 * (q1 - quad_width) + 5] << 2;
> +
> + if ((ret = jpeg2000_decode_sig_emb(s, mel_state,
> mel_stream, vlc_stream,
> + dec_CxtVLC_table1,
> Dcup, sig_pat, res_off,
> + emb_pat_k, emb_pat_1,
> J2K_Q1, context1, Lcup,
> + Pcup))
> + < 0)
> + goto free;
> +
> + for (int i = 0; i < 4; i++)
> + sigma_n[4 * q1 + i] = (sig_pat[J2K_Q1] >> i) & 1;
> +
> + u[J2K_Q1] = 0;
> +
> + /* Recover mag_sgn value */
> + if (res_off[J2K_Q1] == 1) {
> + u_pfx[J2K_Q1] = vlc_decode_u_prefix(vlc_stream,
> vlc_buf);
> + u_sfx[J2K_Q1] = vlc_decode_u_suffix(vlc_stream,
> u_pfx[J2K_Q1], vlc_buf);
> + u_ext[J2K_Q1] = vlc_decode_u_extension(vlc_stream,
> u_sfx[J2K_Q1], vlc_buf);
> +
> + u[J2K_Q1] = u_pfx[J2K_Q1] + u_sfx[J2K_Q1] +
> (u_ext[J2K_Q1] << 2);
> + }
> +
> + sp = sig_pat[J2K_Q1];
> +
> + gamma[J2K_Q1] = 1;
> +
> + if (sp == 0 || sp == 1 || sp == 2 || sp == 4 || sp == 8)
> + gamma[J2K_Q1] = 0;
> +
> + E_n[J2K_Q1] = E[4 * (q1 - quad_width) + 1];
> +
> + E_ne[J2K_Q1] = E[4 * (q1 - quad_width) + 3];
> +
> + E_nw[J2K_Q1] = (!is_divisible(q1, c)) * E[FFMAX((4 * (q1
> - quad_width) - 1), 0)];
> +
> + E_nf[J2K_Q1] = (!is_divisible(q1 + 1, c)) * E[4 * (q1 -
> quad_width) + 5];
> +
> + max_e[J2K_Q1] = FFMAX(E_nw[J2K_Q1], FFMAX3(E_n[J2K_Q1],
> E_ne[J2K_Q1], E_nf[J2K_Q1]));
> +
> + kappa[J2K_Q1] = FFMAX(1, gamma[J2K_Q1] * (max_e[J2K_Q1]
> - 1));
> +
> + U[J2K_Q1] = kappa[J2K_Q1] + u[J2K_Q1];
> +
> + for (int i = 0; i < 4; i++)
> + m[J2K_Q1][i] = sigma_n[4 * q1 + i] * U[J2K_Q1] -
> ((emb_pat_k[J2K_Q1] >> i) & 1);
> +
> + recover_mag_sgn(mag_sgn_stream, J2K_Q1, q1, m_n,
> known_1, emb_pat_1, v, m,
> + E, mu_n, Dcup, Pcup, pLSB);
> + q += 1;
> + }
> + }
> + // convert to raster-scan
Could this be done all in one go in the loop above? Writing to mu then
reading from it later is not very cache friendly.
No further comments for now. Might re-read it later.
/Tomas
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next prev parent reply other threads:[~2022-12-02 18:46 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-02 18:11 etemesicaleb
2022-12-02 18:46 ` Tomas Härdin [this message]
2022-12-02 19:34 ` Caleb Etemesi
2022-12-02 19:35 ` Caleb Etemesi
2022-12-12 18:40 ` Pierre-Anthony Lemieux
2022-12-14 17:39 ` Tomas Härdin
2022-12-28 20:20 etemesicaleb
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