avcodec/exr: add lut oriented half to float conversion code

2026-05-01 06:13:08 +08:00 · 2021-02-28 12:44:25 +01:00
parent cf2f8dcc6a
commit 6cc3ba4be6
2 changed files with 103 additions and 73 deletions
--- a/libavcodec/half2float.h
+++ b/libavcodec/half2float.h
@@ -0,0 +1,74 @@
+/*
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVCODEC_HALF2FLOAT_H
+#define AVCODEC_HALF2FLOAT_H
+
+#include <stdint.h>
+
+static uint32_t convertmantissa(uint32_t i)
+{
+    uint32_t m = i << 13; // Zero pad mantissa bits
+    uint32_t e = 0; // Zero exponent
+
+    while (!(m & 0x00800000UL)){ // While not normalized
+        e -= 0x00800000UL; // Decrement exponent (1<<23)
+        m <<= 1; // Shift mantissa
+    }
+
+    m &= ~0x00800000UL; // Clear leading 1 bit
+    e +=  0x38800000UL; // Adjust bias ((127-14)<<23)
+
+    return m | e; // Return combined number
+}
+
+static void half2float_table(uint32_t *mantissatable, uint32_t *exponenttable,
+                             uint16_t *offsettable)
+{
+    mantissatable[0] = 0;
+    for (int i = 1; i < 1024; i++)
+        mantissatable[i] = convertmantissa(i);
+    for (int i = 1024; i < 2048; i++)
+        mantissatable[i] = 0x38000000UL + ((i - 1024) << 13UL);
+
+    exponenttable[0] = 0;
+    for (int i = 1; i < 31; i++)
+        exponenttable[i] = i << 23;
+    for (int i = 33; i < 63; i++)
+        exponenttable[i] = 0x80000000UL + ((i - 32) << 23UL);
+    exponenttable[31]= 0x47800000UL;
+    exponenttable[32]= 0x80000000UL;
+    exponenttable[63]= 0xC7800000UL;
+
+    offsettable[0] = 0;
+    for (int i = 1; i < 64; i++)
+        offsettable[i] = 1024;
+    offsettable[32] = 0;
+}
+
+static uint32_t half2float(uint16_t h, uint32_t *mantissatable, uint32_t *exponenttable,
+                           uint16_t *offsettable)
+{
+    uint32_t f;
+
+    f = mantissatable[offsettable[h >> 10] + (h & 0x3ff)] + exponenttable[h >> 10];
+
+    return f;
+}
+
+#endif /* AVCODEC_HALF2FLOAT_H */