i965: Have brw_imm_vf4() take the vector components as integer values.

Reviewed-by: Paul Berry <stereotype441@gmail.com>

src/mesa/drivers/dri/i965/brw_clip_util.c

@@ -224,7 +224,7 @@ void brw_clip_interp_vertex( struct brw_clip_compile *c,
               vec1(t_nopersp),
               brw_imm_f(0));
       brw_IF(p, BRW_EXECUTE_1);
-      brw_MOV(p, t_nopersp, brw_imm_vf4(VF_ONE, VF_ZERO, VF_ZERO, VF_ZERO));
+      brw_MOV(p, t_nopersp, brw_imm_vf4(1, 0, 0, 0));
       brw_ENDIF(p);
 
       /* Now compute t_nopersp = t_nopersp.y/t_nopersp.x and broadcast it. */

src/mesa/drivers/dri/i965/brw_reg.h

@@ -43,6 +43,7 @@
 #define BRW_REG_H
 
 #include <stdbool.h>
+#include "main/imports.h"
 #include "program/prog_instruction.h"
 #include "brw_defines.h"
 
@@ -510,19 +511,38 @@ brw_imm_vf(unsigned v)
    return imm;
 }
 
-#define VF_ZERO 0x0
-#define VF_ONE  0x30
-#define VF_NEG  (1<<7)
-
-static inline struct brw_reg
-brw_imm_vf4(unsigned v0, unsigned v1, unsigned v2, unsigned v3)
+/**
+ * Convert an integer into a "restricted" 8-bit float, used in vector
+ * immediates.  The 8-bit floating point format has a sign bit, an
+ * excess-3 3-bit exponent, and a 4-bit mantissa.  All integer values
+ * from -31 to 31 can be represented exactly.
+ */
+static inline uint8_t
+int_to_float8(int x)
 {
-   struct brw_reg imm = brw_imm_reg(BRW_REGISTER_TYPE_VF);
-   imm.vstride = BRW_VERTICAL_STRIDE_0;
-   imm.width = BRW_WIDTH_4;
-   imm.hstride = BRW_HORIZONTAL_STRIDE_1;
-   imm.dw1.ud = ((v0 << 0) | (v1 << 8) | (v2 << 16) | (v3 << 24));
-   return imm;
+   if (x == 0) {
+      return 0;
+   } else if (x < 0) {
+      return 1 << 7 | int_to_float8(-x);
+   } else {
+      const unsigned exponent = _mesa_logbase2(x);
+      const unsigned mantissa = (x - (1 << exponent)) << (4 - exponent);
+      assert(exponent <= 4);
+      return (exponent + 3) << 4 | mantissa;
+   }
+}
+
+/**
+ * Construct a floating-point packed vector immediate from its integer
+ * values. \sa int_to_float8()
+ */
+static inline struct brw_reg
+brw_imm_vf4(int v0, int v1, int v2, int v3)
+{
+   return brw_imm_vf((int_to_float8(v0) << 0) |
+                     (int_to_float8(v1) << 8) |
+                     (int_to_float8(v2) << 16) |
+                     (int_to_float8(v3) << 24));
 }