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vc4: Apply a Newton-Raphson step to improve RSQ

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Fixes all the piglit built-in-functions/*sqrt tests, among others.
This commit is contained in:
Eric Anholt 2014-10-17 15:28:02 +01:00
parent 1fc124b80f
commit 15eb4c59f6
1 changed files with 20 additions and 2 deletions
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22
src/gallium/drivers/vc4/vc4_program.c
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@ -312,6 +312,25 @@ tgsi_to_qir_rcp(struct vc4_compile *c,
return r;
}
static struct qreg
tgsi_to_qir_rsq(struct vc4_compile *c,
struct tgsi_full_instruction *tgsi_inst,
enum qop op, struct qreg *src, int i)
{
struct qreg x = src[0 * 4 + 0];
struct qreg r = qir_RSQ(c, x);
/* Apply a Newton-Raphson step to improve the accuracy. */
r = qir_FMUL(c, r, qir_FSUB(c,
qir_uniform_f(c, 1.5),
qir_FMUL(c,
qir_uniform_f(c, 0.5),
qir_FMUL(c, x,
qir_FMUL(c, r, r)))));
return r;
}
static struct qreg
qir_srgb_decode(struct vc4_compile *c, struct qreg srgb)
{
@ -1165,7 +1184,6 @@ emit_tgsi_instruction(struct vc4_compile *c,
[TGSI_OPCODE_IDIV] = { 0, tgsi_to_qir_idiv },
[TGSI_OPCODE_INEG] = { 0, tgsi_to_qir_ineg },
[TGSI_OPCODE_RSQ] = { QOP_RSQ, tgsi_to_qir_alu },
[TGSI_OPCODE_SEQ] = { 0, tgsi_to_qir_seq },
[TGSI_OPCODE_SNE] = { 0, tgsi_to_qir_sne },
[TGSI_OPCODE_SGE] = { 0, tgsi_to_qir_sge },
@ -1182,7 +1200,7 @@ emit_tgsi_instruction(struct vc4_compile *c,
[TGSI_OPCODE_CMP] = { 0, tgsi_to_qir_cmp },
[TGSI_OPCODE_MAD] = { 0, tgsi_to_qir_mad },
[TGSI_OPCODE_RCP] = { QOP_RCP, tgsi_to_qir_rcp },
[TGSI_OPCODE_RSQ] = { QOP_RSQ, tgsi_to_qir_scalar },
[TGSI_OPCODE_RSQ] = { QOP_RSQ, tgsi_to_qir_rsq },
[TGSI_OPCODE_EX2] = { QOP_EXP2, tgsi_to_qir_scalar },
[TGSI_OPCODE_LG2] = { QOP_LOG2, tgsi_to_qir_scalar },
[TGSI_OPCODE_LRP] = { 0, tgsi_to_qir_lrp },