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/**
Copyright (c) Scott Gasch
Module Name:
nnueeval.c
Abstract:
The FC head (2*L1 -> L2 -> L3 -> 1) that sits on top of the two
accumulator halves maintained by nnueaccum.c, plus the loader for
a real trained checkpoint exported by annotate_pgns/
export_nnue_weights.py. Reference-only right now -- not wired
into Eval()/search, just enough to prove weights can actually be
loaded and forward-propagated against a real position (see
command.c's "nnue load"/"dump nnueeval").
Not hot-path (unlike nnueaccum.c's Add/Remove, called from every
MakeMove) -- this only runs once per position actually evaluated,
so it's written straight-line/unoptimized, same spirit as
nnuefeatures.c's reference dump.
Author:
Scott Gasch ([email protected]) 15 Oct 2026
**/
#include "chess.h"
float g_rgfNnueFc1Weight[NNUE_L2][2 * NNUE_ACCUMULATOR_SIZE];
float g_rgfNnueFc1Bias[NNUE_L2];
float g_rgfNnueFc2Weight[NNUE_L3][NNUE_L2];
float g_rgfNnueFc2Bias[NNUE_L3];
float g_rgfNnueFc3Weight[NNUE_L3];
float g_rgfNnueFc3Bias;
FLAG g_fNnueWeightsLoaded = FALSE;
FLAG g_fUseNnueEval = FALSE;
FLAG
NnueLoadWeights(CHAR *szFilename)
/**
Routine description:
Loads a weights file written by annotate_pgns/
export_nnue_weights.py: a 4-byte magic, a 4xuint32 dimension
header (sanity-checked against this build's own NNUE_DIMENSIONS/
NNUE_ACCUMULATOR_SIZE/NNUE_L2/NNUE_L3 so a mismatched export can't
silently misread), then the eight weight/bias arrays in a fixed
order. g_fNnueWeightsLoaded is FALSE on any failure (including a
partial read -- no half-loaded state is left live).
Parameters:
CHAR *szFilename
Return value:
FLAG : TRUE on success
**/
{
FILE *fp;
CHAR szMagic[4];
ULONG rguDims[4];
g_fNnueWeightsLoaded = FALSE;
fp = fopen(szFilename, "rb");
if (NULL == fp)
{
Trace("NnueLoadWeights: could not open %s\n", szFilename);
return FALSE;
}
if ((1 != fread(szMagic, 4, 1, fp)) ||
(0 != memcmp(szMagic, "NNU1", 4)))
{
Trace("NnueLoadWeights: %s is not a valid NNUE weights file "
"(bad magic)\n", szFilename);
fclose(fp);
return FALSE;
}
if (1 != fread(rguDims, sizeof(rguDims), 1, fp))
{
Trace("NnueLoadWeights: %s truncated (header)\n", szFilename);
fclose(fp);
return FALSE;
}
if ((rguDims[0] != NNUE_DIMENSIONS) ||
(rguDims[1] != NNUE_ACCUMULATOR_SIZE) ||
(rguDims[2] != NNUE_L2) ||
(rguDims[3] != NNUE_L3))
{
Trace("NnueLoadWeights: %s dims (%lu,%lu,%lu,%lu) don't match "
"this build's (%lu,%lu,%lu,%lu)\n", szFilename,
rguDims[0], rguDims[1], rguDims[2], rguDims[3],
(ULONG)NNUE_DIMENSIONS, (ULONG)NNUE_ACCUMULATOR_SIZE,
(ULONG)NNUE_L2, (ULONG)NNUE_L3);
fclose(fp);
return FALSE;
}
#define READ_OR_FAIL(ptr, count) \
do { \
if ((size_t)(count) != fread((ptr), sizeof(float), (count), fp)) \
{ \
Trace("NnueLoadWeights: %s truncated\n", szFilename); \
fclose(fp); \
return FALSE; \
} \
} while (0)
READ_OR_FAIL(g_rgfNnueWeight, (size_t)NNUE_DIMENSIONS * NNUE_ACCUMULATOR_SIZE);
READ_OR_FAIL(g_rgfNnueBias, NNUE_ACCUMULATOR_SIZE);
READ_OR_FAIL(g_rgfNnueFc1Weight, (size_t)NNUE_L2 * 2 * NNUE_ACCUMULATOR_SIZE);
READ_OR_FAIL(g_rgfNnueFc1Bias, NNUE_L2);
READ_OR_FAIL(g_rgfNnueFc2Weight, (size_t)NNUE_L3 * NNUE_L2);
READ_OR_FAIL(g_rgfNnueFc2Bias, NNUE_L3);
READ_OR_FAIL(g_rgfNnueFc3Weight, NNUE_L3);
READ_OR_FAIL(&g_rgfNnueFc3Bias, 1);
#undef READ_OR_FAIL
fclose(fp);
g_fNnueWeightsLoaded = TRUE;
Trace("NnueLoadWeights: loaded %s\n", szFilename);
return TRUE;
}
SCORE
NnueForward(SEARCHER_THREAD_CONTEXT *ctx)
/**
Routine description:
Runs the full forward pass -- ReLU(accumulator), own-perspective-
first concatenation by side to move (matching nnue_model.py's own
convention so the single scalar output is side-to-move-relative
by construction), then the dense 2*L1 -> L2 -> L3 -> 1 FC head --
against ctx->sNnueAccum as it currently stands. Caller's
responsibility to make sure that accumulator is actually correct
for ctx->sPosition first (a fresh NnueAccumRecompute for both
colors, if there's any doubt) -- this function trusts it as
given.
Parameters:
SEARCHER_THREAD_CONTEXT *ctx
Return value:
SCORE : side-to-move-relative, in centipawns (the net's own raw
output is in pawn units, same scale as the training label's
score field -- see annotate_pgns/fit_k_and_label.py)
**/
{
POSITION *pos = &ctx->sPosition;
ULONG uStm = pos->uToMove;
ULONG uOther = FLIP(uStm);
float rgfConcat[2 * NNUE_ACCUMULATOR_SIZE];
float rgfL2[NNUE_L2];
float rgfL3[NNUE_L3];
float fOut;
ULONG i, j;
for (i = 0; i < NNUE_ACCUMULATOR_SIZE; i++)
{
float v = ctx->sNnueAccum[uStm].rgfValue[i];
rgfConcat[i] = (v > 0.0f) ? v : 0.0f;
}
for (i = 0; i < NNUE_ACCUMULATOR_SIZE; i++)
{
float v = ctx->sNnueAccum[uOther].rgfValue[i];
rgfConcat[NNUE_ACCUMULATOR_SIZE + i] = (v > 0.0f) ? v : 0.0f;
}
for (j = 0; j < NNUE_L2; j++)
{
float s = g_rgfNnueFc1Bias[j];
for (i = 0; i < 2 * NNUE_ACCUMULATOR_SIZE; i++)
{
s += g_rgfNnueFc1Weight[j][i] * rgfConcat[i];
}
rgfL2[j] = (s > 0.0f) ? s : 0.0f;
}
for (j = 0; j < NNUE_L3; j++)
{
float s = g_rgfNnueFc2Bias[j];
for (i = 0; i < NNUE_L2; i++)
{
s += g_rgfNnueFc2Weight[j][i] * rgfL2[i];
}
rgfL3[j] = (s > 0.0f) ? s : 0.0f;
}
fOut = g_rgfNnueFc3Bias;
for (i = 0; i < NNUE_L3; i++)
{
fOut += g_rgfNnueFc3Weight[i] * rgfL3[i];
}
return (SCORE)(fOut * 100.0f);
}
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