Detect fp_exceptions in FADD

Defined several floating-point exceptions and a fflag_mask in riscv_private.h
It will now detect invalid_op, overflow, and inexact  during execution of FADD and set the corresponding bit in FCSR.
Modify csr_get_ptr and csr_csrrs so that insn CSRRS can deal with CSR_FFLAGS.

New test passed:
fadd_b10-01
fadd_b11-01
fadd_b12-01
fadd_b13-01
fadd_b7-01

Author: 2011eric

emulate.c

@@ -617,6 +617,8 @@ static uint32_t *csr_get_ptr(struct riscv_t *rv, uint32_t csr)
     case CSR_MIP:
         return (uint32_t *) (&rv->csr_mip);
 #ifdef ENABLE_RV32F
+    case CSR_FFLAGS:
+        return (uint32_t *) (&rv->csr_fcsr);
     case CSR_FCSR:
         return (uint32_t *) (&rv->csr_fcsr);
 #endif
@@ -651,7 +653,7 @@ static uint32_t csr_csrrs(struct riscv_t *rv, uint32_t csr, uint32_t val)
     if (!c)
         return 0;
 
-    const uint32_t out = *c;
+    const uint32_t out = (csr == CSR_FFLAGS) ? *c & FFLAG_MASK : *c;
     if (csr_is_writable(csr))
         *c |= val;
 
@@ -901,10 +903,25 @@ static bool op_fp(struct riscv_t *rv, uint32_t insn)
     /* dispatch based on func7 (low 2 bits are width) */
     switch (funct7) {
     case 0b0000000: /* FADD */
-        rv->F[rd] = rv->F[rs1] + rv->F[rs2];
+        if (isnan(rv->F[rs1]) || isnan(rv->F[rs2]) ||
+            isnan(rv->F[rs1] + rv->F[rs2])) {
+            /* raise invalid operation */
+            *((uint32_t *) &rv->F[rd]) = RV_NAN;
+            rv->csr_fcsr |= FFLAG_INVALID_OP;
+        } else {
+            rv->F[rd] = rv->F[rs1] + rv->F[rs2];
+        }
+        if (isinff(rv->F[rd])) {
+            rv->csr_fcsr |= FFLAG_OVERFLOW;
+            rv->csr_fcsr |= FFLAG_INEXACT;
+        }
         break;
     case 0b0000100: /* FSUB */
-        rv->F[rd] = rv->F[rs1] - rv->F[rs2];
+        if (isnan(rv->F[rs1]) || isnan(rv->F[rs2])) {
+            *((uint32_t *) &rv->F[rd]) = RV_NAN;
+        } else {
+            rv->F[rd] = rv->F[rs1] - rv->F[rs2];
+        }
         break;
     case 0b0001000: /* FMUL */
         rv->F[rd] = rv->F[rs1] * rv->F[rs2];

riscv_private.h

@@ -102,10 +102,19 @@ enum {
 
 #ifdef ENABLE_RV32F
 enum {
-    //             ....xxxx....xxxx....xxxx....xxxx
-    FMASK_SIGN = 0b10000000000000000000000000000000,
-    FMASK_EXPN = 0b01111111100000000000000000000000,
-    FMASK_FRAC = 0b00000000011111111111111111111111,
+    //                    ....xxxx....xxxx....xxxx....xxxx
+    FMASK_SIGN        = 0b10000000000000000000000000000000,
+    FMASK_EXPN        = 0b01111111100000000000000000000000,
+    FMASK_FRAC        = 0b00000000011111111111111111111111,
+    //                    ....xxxx....xxxx....xxxx....xxxx
+    FFLAG_MASK        = 0b00000000000000000000000000011111,
+    FFLAG_INVALID_OP  = 0b00000000000000000000000000010000,
+    FFLAG_DIV_BY_ZERO = 0b00000000000000000000000000001000,
+    FFLAG_OVERFLOW    = 0b00000000000000000000000000000100,
+    FFLAG_UNDERFLOW   = 0b00000000000000000000000000000010,
+    FFLAG_INEXACT     = 0b00000000000000000000000000000001,
+    //                    ....xxxx....xxxx....xxxx....xxxx
+    RV_NAN            = 0b01111111110000000000000000000000
 };
 #endif
 /* clang-format off */