1cabdff1aSopenharmony_ci/* 2cabdff1aSopenharmony_ci * Copyright (c) 2016 Clément Bœsch <clement stupeflix.com> 3cabdff1aSopenharmony_ci * Copyright (c) 2019-2021 Sebastian Pop <spop@amazon.com> 4cabdff1aSopenharmony_ci * Copyright (c) 2022 Jonathan Swinney <jswinney@amazon.com> 5cabdff1aSopenharmony_ci * 6cabdff1aSopenharmony_ci * This file is part of FFmpeg. 7cabdff1aSopenharmony_ci * 8cabdff1aSopenharmony_ci * FFmpeg is free software; you can redistribute it and/or 9cabdff1aSopenharmony_ci * modify it under the terms of the GNU Lesser General Public 10cabdff1aSopenharmony_ci * License as published by the Free Software Foundation; either 11cabdff1aSopenharmony_ci * version 2.1 of the License, or (at your option) any later version. 12cabdff1aSopenharmony_ci * 13cabdff1aSopenharmony_ci * FFmpeg is distributed in the hope that it will be useful, 14cabdff1aSopenharmony_ci * but WITHOUT ANY WARRANTY; without even the implied warranty of 15cabdff1aSopenharmony_ci * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 16cabdff1aSopenharmony_ci * Lesser General Public License for more details. 17cabdff1aSopenharmony_ci * 18cabdff1aSopenharmony_ci * You should have received a copy of the GNU Lesser General Public 19cabdff1aSopenharmony_ci * License along with FFmpeg; if not, write to the Free Software 20cabdff1aSopenharmony_ci * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 21cabdff1aSopenharmony_ci */ 22cabdff1aSopenharmony_ci 23cabdff1aSopenharmony_ci#include "libavutil/aarch64/asm.S" 24cabdff1aSopenharmony_ci 25cabdff1aSopenharmony_ci/* 26cabdff1aSopenharmony_ci;----------------------------------------------------------------------------- 27cabdff1aSopenharmony_ci; horizontal line scaling 28cabdff1aSopenharmony_ci; 29cabdff1aSopenharmony_ci; void hscale<source_width>to<intermediate_nbits>_<filterSize>_<opt> 30cabdff1aSopenharmony_ci; (SwsContext *c, int{16,32}_t *dst, 31cabdff1aSopenharmony_ci; int dstW, const uint{8,16}_t *src, 32cabdff1aSopenharmony_ci; const int16_t *filter, 33cabdff1aSopenharmony_ci; const int32_t *filterPos, int filterSize); 34cabdff1aSopenharmony_ci; 35cabdff1aSopenharmony_ci; Scale one horizontal line. Input is either 8-bit width or 16-bit width 36cabdff1aSopenharmony_ci; ($source_width can be either 8, 9, 10 or 16, difference is whether we have to 37cabdff1aSopenharmony_ci; downscale before multiplying). Filter is 14 bits. Output is either 15 bits 38cabdff1aSopenharmony_ci; (in int16_t) or 19 bits (in int32_t), as given in $intermediate_nbits. Each 39cabdff1aSopenharmony_ci; output pixel is generated from $filterSize input pixels, the position of 40cabdff1aSopenharmony_ci; the first pixel is given in filterPos[nOutputPixel]. 41cabdff1aSopenharmony_ci;----------------------------------------------------------------------------- */ 42cabdff1aSopenharmony_ci 43cabdff1aSopenharmony_cifunction ff_hscale8to15_X8_neon, export=1 44cabdff1aSopenharmony_ci sbfiz x7, x6, #1, #32 // filterSize*2 (*2 because int16) 45cabdff1aSopenharmony_ci1: ldr w8, [x5], #4 // filterPos[idx] 46cabdff1aSopenharmony_ci ldr w0, [x5], #4 // filterPos[idx + 1] 47cabdff1aSopenharmony_ci ldr w11, [x5], #4 // filterPos[idx + 2] 48cabdff1aSopenharmony_ci ldr w9, [x5], #4 // filterPos[idx + 3] 49cabdff1aSopenharmony_ci mov x16, x4 // filter0 = filter 50cabdff1aSopenharmony_ci add x12, x16, x7 // filter1 = filter0 + filterSize*2 51cabdff1aSopenharmony_ci add x13, x12, x7 // filter2 = filter1 + filterSize*2 52cabdff1aSopenharmony_ci add x4, x13, x7 // filter3 = filter2 + filterSize*2 53cabdff1aSopenharmony_ci movi v0.2D, #0 // val sum part 1 (for dst[0]) 54cabdff1aSopenharmony_ci movi v1.2D, #0 // val sum part 2 (for dst[1]) 55cabdff1aSopenharmony_ci movi v2.2D, #0 // val sum part 3 (for dst[2]) 56cabdff1aSopenharmony_ci movi v3.2D, #0 // val sum part 4 (for dst[3]) 57cabdff1aSopenharmony_ci add x17, x3, w8, UXTW // srcp + filterPos[0] 58cabdff1aSopenharmony_ci add x8, x3, w0, UXTW // srcp + filterPos[1] 59cabdff1aSopenharmony_ci add x0, x3, w11, UXTW // srcp + filterPos[2] 60cabdff1aSopenharmony_ci add x11, x3, w9, UXTW // srcp + filterPos[3] 61cabdff1aSopenharmony_ci mov w15, w6 // filterSize counter 62cabdff1aSopenharmony_ci2: ld1 {v4.8B}, [x17], #8 // srcp[filterPos[0] + {0..7}] 63cabdff1aSopenharmony_ci ld1 {v5.8H}, [x16], #16 // load 8x16-bit filter values, part 1 64cabdff1aSopenharmony_ci ld1 {v6.8B}, [x8], #8 // srcp[filterPos[1] + {0..7}] 65cabdff1aSopenharmony_ci ld1 {v7.8H}, [x12], #16 // load 8x16-bit at filter+filterSize 66cabdff1aSopenharmony_ci uxtl v4.8H, v4.8B // unpack part 1 to 16-bit 67cabdff1aSopenharmony_ci smlal v0.4S, v4.4H, v5.4H // v0 accumulates srcp[filterPos[0] + {0..3}] * filter[{0..3}] 68cabdff1aSopenharmony_ci smlal2 v0.4S, v4.8H, v5.8H // v0 accumulates srcp[filterPos[0] + {4..7}] * filter[{4..7}] 69cabdff1aSopenharmony_ci ld1 {v16.8B}, [x0], #8 // srcp[filterPos[2] + {0..7}] 70cabdff1aSopenharmony_ci ld1 {v17.8H}, [x13], #16 // load 8x16-bit at filter+2*filterSize 71cabdff1aSopenharmony_ci uxtl v6.8H, v6.8B // unpack part 2 to 16-bit 72cabdff1aSopenharmony_ci smlal v1.4S, v6.4H, v7.4H // v1 accumulates srcp[filterPos[1] + {0..3}] * filter[{0..3}] 73cabdff1aSopenharmony_ci uxtl v16.8H, v16.8B // unpack part 3 to 16-bit 74cabdff1aSopenharmony_ci smlal v2.4S, v16.4H, v17.4H // v2 accumulates srcp[filterPos[2] + {0..3}] * filter[{0..3}] 75cabdff1aSopenharmony_ci smlal2 v2.4S, v16.8H, v17.8H // v2 accumulates srcp[filterPos[2] + {4..7}] * filter[{4..7}] 76cabdff1aSopenharmony_ci ld1 {v18.8B}, [x11], #8 // srcp[filterPos[3] + {0..7}] 77cabdff1aSopenharmony_ci smlal2 v1.4S, v6.8H, v7.8H // v1 accumulates srcp[filterPos[1] + {4..7}] * filter[{4..7}] 78cabdff1aSopenharmony_ci ld1 {v19.8H}, [x4], #16 // load 8x16-bit at filter+3*filterSize 79cabdff1aSopenharmony_ci subs w15, w15, #8 // j -= 8: processed 8/filterSize 80cabdff1aSopenharmony_ci uxtl v18.8H, v18.8B // unpack part 4 to 16-bit 81cabdff1aSopenharmony_ci smlal v3.4S, v18.4H, v19.4H // v3 accumulates srcp[filterPos[3] + {0..3}] * filter[{0..3}] 82cabdff1aSopenharmony_ci smlal2 v3.4S, v18.8H, v19.8H // v3 accumulates srcp[filterPos[3] + {4..7}] * filter[{4..7}] 83cabdff1aSopenharmony_ci b.gt 2b // inner loop if filterSize not consumed completely 84cabdff1aSopenharmony_ci addp v0.4S, v0.4S, v1.4S // part01 horizontal pair adding 85cabdff1aSopenharmony_ci addp v2.4S, v2.4S, v3.4S // part23 horizontal pair adding 86cabdff1aSopenharmony_ci addp v0.4S, v0.4S, v2.4S // part0123 horizontal pair adding 87cabdff1aSopenharmony_ci subs w2, w2, #4 // dstW -= 4 88cabdff1aSopenharmony_ci sqshrn v0.4H, v0.4S, #7 // shift and clip the 2x16-bit final values 89cabdff1aSopenharmony_ci st1 {v0.4H}, [x1], #8 // write to destination part0123 90cabdff1aSopenharmony_ci b.gt 1b // loop until end of line 91cabdff1aSopenharmony_ci ret 92cabdff1aSopenharmony_ciendfunc 93cabdff1aSopenharmony_ci 94cabdff1aSopenharmony_cifunction ff_hscale8to15_4_neon, export=1 95cabdff1aSopenharmony_ci// x0 SwsContext *c (not used) 96cabdff1aSopenharmony_ci// x1 int16_t *dst 97cabdff1aSopenharmony_ci// x2 int dstW 98cabdff1aSopenharmony_ci// x3 const uint8_t *src 99cabdff1aSopenharmony_ci// x4 const int16_t *filter 100cabdff1aSopenharmony_ci// x5 const int32_t *filterPos 101cabdff1aSopenharmony_ci// x6 int filterSize 102cabdff1aSopenharmony_ci// x8-x15 registers for gathering src data 103cabdff1aSopenharmony_ci 104cabdff1aSopenharmony_ci// v0 madd accumulator 4S 105cabdff1aSopenharmony_ci// v1-v4 filter values (16 bit) 8H 106cabdff1aSopenharmony_ci// v5 madd accumulator 4S 107cabdff1aSopenharmony_ci// v16-v19 src values (8 bit) 8B 108cabdff1aSopenharmony_ci 109cabdff1aSopenharmony_ci// This implementation has 4 sections: 110cabdff1aSopenharmony_ci// 1. Prefetch src data 111cabdff1aSopenharmony_ci// 2. Interleaved prefetching src data and madd 112cabdff1aSopenharmony_ci// 3. Complete madd 113cabdff1aSopenharmony_ci// 4. Complete remaining iterations when dstW % 8 != 0 114cabdff1aSopenharmony_ci 115cabdff1aSopenharmony_ci sub sp, sp, #32 // allocate 32 bytes on the stack 116cabdff1aSopenharmony_ci cmp w2, #16 // if dstW <16, skip to the last block used for wrapping up 117cabdff1aSopenharmony_ci b.lt 2f 118cabdff1aSopenharmony_ci 119cabdff1aSopenharmony_ci // load 8 values from filterPos to be used as offsets into src 120cabdff1aSopenharmony_ci ldp w8, w9, [x5] // filterPos[idx + 0], [idx + 1] 121cabdff1aSopenharmony_ci ldp w10, w11, [x5, #8] // filterPos[idx + 2], [idx + 3] 122cabdff1aSopenharmony_ci ldp w12, w13, [x5, #16] // filterPos[idx + 4], [idx + 5] 123cabdff1aSopenharmony_ci ldp w14, w15, [x5, #24] // filterPos[idx + 6], [idx + 7] 124cabdff1aSopenharmony_ci add x5, x5, #32 // advance filterPos 125cabdff1aSopenharmony_ci 126cabdff1aSopenharmony_ci // gather random access data from src into contiguous memory 127cabdff1aSopenharmony_ci ldr w8, [x3, w8, UXTW] // src[filterPos[idx + 0]][0..3] 128cabdff1aSopenharmony_ci ldr w9, [x3, w9, UXTW] // src[filterPos[idx + 1]][0..3] 129cabdff1aSopenharmony_ci ldr w10, [x3, w10, UXTW] // src[filterPos[idx + 2]][0..3] 130cabdff1aSopenharmony_ci ldr w11, [x3, w11, UXTW] // src[filterPos[idx + 3]][0..3] 131cabdff1aSopenharmony_ci ldr w12, [x3, w12, UXTW] // src[filterPos[idx + 4]][0..3] 132cabdff1aSopenharmony_ci ldr w13, [x3, w13, UXTW] // src[filterPos[idx + 5]][0..3] 133cabdff1aSopenharmony_ci ldr w14, [x3, w14, UXTW] // src[filterPos[idx + 6]][0..3] 134cabdff1aSopenharmony_ci ldr w15, [x3, w15, UXTW] // src[filterPos[idx + 7]][0..3] 135cabdff1aSopenharmony_ci stp w8, w9, [sp] // *scratch_mem = { src[filterPos[idx + 0]][0..3], src[filterPos[idx + 1]][0..3] } 136cabdff1aSopenharmony_ci stp w10, w11, [sp, #8] // *scratch_mem = { src[filterPos[idx + 2]][0..3], src[filterPos[idx + 3]][0..3] } 137cabdff1aSopenharmony_ci stp w12, w13, [sp, #16] // *scratch_mem = { src[filterPos[idx + 4]][0..3], src[filterPos[idx + 5]][0..3] } 138cabdff1aSopenharmony_ci stp w14, w15, [sp, #24] // *scratch_mem = { src[filterPos[idx + 6]][0..3], src[filterPos[idx + 7]][0..3] } 139cabdff1aSopenharmony_ci 140cabdff1aSopenharmony_ci1: 141cabdff1aSopenharmony_ci ld4 {v16.8B, v17.8B, v18.8B, v19.8B}, [sp] // transpose 8 bytes each from src into 4 registers 142cabdff1aSopenharmony_ci 143cabdff1aSopenharmony_ci // load 8 values from filterPos to be used as offsets into src 144cabdff1aSopenharmony_ci ldp w8, w9, [x5] // filterPos[idx + 0][0..3], [idx + 1][0..3], next iteration 145cabdff1aSopenharmony_ci ldp w10, w11, [x5, #8] // filterPos[idx + 2][0..3], [idx + 3][0..3], next iteration 146cabdff1aSopenharmony_ci ldp w12, w13, [x5, #16] // filterPos[idx + 4][0..3], [idx + 5][0..3], next iteration 147cabdff1aSopenharmony_ci ldp w14, w15, [x5, #24] // filterPos[idx + 6][0..3], [idx + 7][0..3], next iteration 148cabdff1aSopenharmony_ci 149cabdff1aSopenharmony_ci movi v0.2D, #0 // Clear madd accumulator for idx 0..3 150cabdff1aSopenharmony_ci movi v5.2D, #0 // Clear madd accumulator for idx 4..7 151cabdff1aSopenharmony_ci 152cabdff1aSopenharmony_ci ld4 {v1.8H, v2.8H, v3.8H, v4.8H}, [x4], #64 // load filter idx + 0..7 153cabdff1aSopenharmony_ci 154cabdff1aSopenharmony_ci add x5, x5, #32 // advance filterPos 155cabdff1aSopenharmony_ci 156cabdff1aSopenharmony_ci // interleaved SIMD and prefetching intended to keep ld/st and vector pipelines busy 157cabdff1aSopenharmony_ci uxtl v16.8H, v16.8B // unsigned extend long, covert src data to 16-bit 158cabdff1aSopenharmony_ci uxtl v17.8H, v17.8B // unsigned extend long, covert src data to 16-bit 159cabdff1aSopenharmony_ci ldr w8, [x3, w8, UXTW] // src[filterPos[idx + 0]], next iteration 160cabdff1aSopenharmony_ci ldr w9, [x3, w9, UXTW] // src[filterPos[idx + 1]], next iteration 161cabdff1aSopenharmony_ci uxtl v18.8H, v18.8B // unsigned extend long, covert src data to 16-bit 162cabdff1aSopenharmony_ci uxtl v19.8H, v19.8B // unsigned extend long, covert src data to 16-bit 163cabdff1aSopenharmony_ci ldr w10, [x3, w10, UXTW] // src[filterPos[idx + 2]], next iteration 164cabdff1aSopenharmony_ci ldr w11, [x3, w11, UXTW] // src[filterPos[idx + 3]], next iteration 165cabdff1aSopenharmony_ci 166cabdff1aSopenharmony_ci smlal v0.4S, v1.4H, v16.4H // multiply accumulate inner loop j = 0, idx = 0..3 167cabdff1aSopenharmony_ci smlal v0.4S, v2.4H, v17.4H // multiply accumulate inner loop j = 1, idx = 0..3 168cabdff1aSopenharmony_ci ldr w12, [x3, w12, UXTW] // src[filterPos[idx + 4]], next iteration 169cabdff1aSopenharmony_ci ldr w13, [x3, w13, UXTW] // src[filterPos[idx + 5]], next iteration 170cabdff1aSopenharmony_ci smlal v0.4S, v3.4H, v18.4H // multiply accumulate inner loop j = 2, idx = 0..3 171cabdff1aSopenharmony_ci smlal v0.4S, v4.4H, v19.4H // multiply accumulate inner loop j = 3, idx = 0..3 172cabdff1aSopenharmony_ci ldr w14, [x3, w14, UXTW] // src[filterPos[idx + 6]], next iteration 173cabdff1aSopenharmony_ci ldr w15, [x3, w15, UXTW] // src[filterPos[idx + 7]], next iteration 174cabdff1aSopenharmony_ci 175cabdff1aSopenharmony_ci smlal2 v5.4S, v1.8H, v16.8H // multiply accumulate inner loop j = 0, idx = 4..7 176cabdff1aSopenharmony_ci smlal2 v5.4S, v2.8H, v17.8H // multiply accumulate inner loop j = 1, idx = 4..7 177cabdff1aSopenharmony_ci stp w8, w9, [sp] // *scratch_mem = { src[filterPos[idx + 0]][0..3], src[filterPos[idx + 1]][0..3] } 178cabdff1aSopenharmony_ci stp w10, w11, [sp, #8] // *scratch_mem = { src[filterPos[idx + 2]][0..3], src[filterPos[idx + 3]][0..3] } 179cabdff1aSopenharmony_ci smlal2 v5.4S, v3.8H, v18.8H // multiply accumulate inner loop j = 2, idx = 4..7 180cabdff1aSopenharmony_ci smlal2 v5.4S, v4.8H, v19.8H // multiply accumulate inner loop j = 3, idx = 4..7 181cabdff1aSopenharmony_ci stp w12, w13, [sp, #16] // *scratch_mem = { src[filterPos[idx + 4]][0..3], src[filterPos[idx + 5]][0..3] } 182cabdff1aSopenharmony_ci stp w14, w15, [sp, #24] // *scratch_mem = { src[filterPos[idx + 6]][0..3], src[filterPos[idx + 7]][0..3] } 183cabdff1aSopenharmony_ci 184cabdff1aSopenharmony_ci sub w2, w2, #8 // dstW -= 8 185cabdff1aSopenharmony_ci sqshrn v0.4H, v0.4S, #7 // shift and clip the 2x16-bit final values 186cabdff1aSopenharmony_ci sqshrn v1.4H, v5.4S, #7 // shift and clip the 2x16-bit final values 187cabdff1aSopenharmony_ci st1 {v0.4H, v1.4H}, [x1], #16 // write to dst[idx + 0..7] 188cabdff1aSopenharmony_ci cmp w2, #16 // continue on main loop if there are at least 16 iterations left 189cabdff1aSopenharmony_ci b.ge 1b 190cabdff1aSopenharmony_ci 191cabdff1aSopenharmony_ci // last full iteration 192cabdff1aSopenharmony_ci ld4 {v16.8B, v17.8B, v18.8B, v19.8B}, [sp] 193cabdff1aSopenharmony_ci ld4 {v1.8H, v2.8H, v3.8H, v4.8H}, [x4], #64 // load filter idx + 0..7 194cabdff1aSopenharmony_ci 195cabdff1aSopenharmony_ci movi v0.2D, #0 // Clear madd accumulator for idx 0..3 196cabdff1aSopenharmony_ci movi v5.2D, #0 // Clear madd accumulator for idx 4..7 197cabdff1aSopenharmony_ci 198cabdff1aSopenharmony_ci uxtl v16.8H, v16.8B // unsigned extend long, covert src data to 16-bit 199cabdff1aSopenharmony_ci uxtl v17.8H, v17.8B // unsigned extend long, covert src data to 16-bit 200cabdff1aSopenharmony_ci uxtl v18.8H, v18.8B // unsigned extend long, covert src data to 16-bit 201cabdff1aSopenharmony_ci uxtl v19.8H, v19.8B // unsigned extend long, covert src data to 16-bit 202cabdff1aSopenharmony_ci 203cabdff1aSopenharmony_ci smlal v0.4S, v1.4H, v16.4H // multiply accumulate inner loop j = 0, idx = 0..3 204cabdff1aSopenharmony_ci smlal v0.4S, v2.4H, v17.4H // multiply accumulate inner loop j = 1, idx = 0..3 205cabdff1aSopenharmony_ci smlal v0.4S, v3.4H, v18.4H // multiply accumulate inner loop j = 2, idx = 0..3 206cabdff1aSopenharmony_ci smlal v0.4S, v4.4H, v19.4H // multiply accumulate inner loop j = 3, idx = 0..3 207cabdff1aSopenharmony_ci 208cabdff1aSopenharmony_ci smlal2 v5.4S, v1.8H, v16.8H // multiply accumulate inner loop j = 0, idx = 4..7 209cabdff1aSopenharmony_ci smlal2 v5.4S, v2.8H, v17.8H // multiply accumulate inner loop j = 1, idx = 4..7 210cabdff1aSopenharmony_ci smlal2 v5.4S, v3.8H, v18.8H // multiply accumulate inner loop j = 2, idx = 4..7 211cabdff1aSopenharmony_ci smlal2 v5.4S, v4.8H, v19.8H // multiply accumulate inner loop j = 3, idx = 4..7 212cabdff1aSopenharmony_ci 213cabdff1aSopenharmony_ci subs w2, w2, #8 // dstW -= 8 214cabdff1aSopenharmony_ci sqshrn v0.4H, v0.4S, #7 // shift and clip the 2x16-bit final values 215cabdff1aSopenharmony_ci sqshrn v1.4H, v5.4S, #7 // shift and clip the 2x16-bit final values 216cabdff1aSopenharmony_ci st1 {v0.4H, v1.4H}, [x1], #16 // write to dst[idx + 0..7] 217cabdff1aSopenharmony_ci 218cabdff1aSopenharmony_ci cbnz w2, 2f // if >0 iterations remain, jump to the wrap up section 219cabdff1aSopenharmony_ci 220cabdff1aSopenharmony_ci add sp, sp, #32 // clean up stack 221cabdff1aSopenharmony_ci ret 222cabdff1aSopenharmony_ci 223cabdff1aSopenharmony_ci // finish up when dstW % 8 != 0 or dstW < 16 224cabdff1aSopenharmony_ci2: 225cabdff1aSopenharmony_ci // load src 226cabdff1aSopenharmony_ci ldr w8, [x5], #4 // filterPos[i] 227cabdff1aSopenharmony_ci add x9, x3, w8, UXTW // calculate the address for src load 228cabdff1aSopenharmony_ci ld1 {v5.S}[0], [x9] // src[filterPos[i] + 0..3] 229cabdff1aSopenharmony_ci // load filter 230cabdff1aSopenharmony_ci ld1 {v6.4H}, [x4], #8 // filter[filterSize * i + 0..3] 231cabdff1aSopenharmony_ci 232cabdff1aSopenharmony_ci uxtl v5.8H, v5.8B // unsigned exten long, convert src data to 16-bit 233cabdff1aSopenharmony_ci smull v0.4S, v5.4H, v6.4H // 4 iterations of src[...] * filter[...] 234cabdff1aSopenharmony_ci addv s0, v0.4S // add up products of src and filter values 235cabdff1aSopenharmony_ci sqshrn h0, s0, #7 // shift and clip the 2x16-bit final value 236cabdff1aSopenharmony_ci st1 {v0.H}[0], [x1], #2 // dst[i] = ... 237cabdff1aSopenharmony_ci sub w2, w2, #1 // dstW-- 238cabdff1aSopenharmony_ci cbnz w2, 2b 239cabdff1aSopenharmony_ci 240cabdff1aSopenharmony_ci add sp, sp, #32 // clean up stack 241cabdff1aSopenharmony_ci ret 242cabdff1aSopenharmony_ciendfunc 243