Implement fsqrt

ish-app · Nov 16, 2018 · 57d3367 · 57d3367
1 parent aaa5015
commit 57d3367
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Showing 7 changed files with 25 additions and 0 deletions.
diff --git a/emu/decode.h b/emu/decode.h
@@ -621,6 +621,7 @@ __no_instrument DECODER_RET glue(DECODER_NAME, OP_SIZE)(DECODER_ARGS) {
                     case 0xd960: TRACE("f2xm1"); F2XM1(); break;
                     case 0xd961: TRACE("fyl2x"); FYL2X(); break;
                     case 0xd970: TRACE("fprem"); FPREM(); break;
+                    case 0xd972: TRACE("fsqrt"); FSQRT(); break;
                     case 0xd974: TRACE("frndint"); FRNDINT(); break;
                     case 0xdf40: TRACE("fnstsw ax"); FSTSW(reg_a); break;
                     default: TRACE("undefined"); UNDEFINED;

diff --git a/emu/float80.c b/emu/float80.c
@@ -473,3 +473,19 @@ float80 f80_log2(float80 x) {
     return res;
 }
 
+float80 f80_sqrt(float80 x) {
+    if (f80_isnan(x) || x.sign)
+        return F80_NAN;
+    // for a rough guess, just cut the exponent by 2
+    float80 guess = x;
+    guess.exp = bias(unbias(guess.exp) / 2);
+    // now converge on the answer, using what newton's method
+    float80 old_guess;
+    float80 two = f80_from_int(2);
+    int i = 0;
+    do {
+        old_guess = guess;
+        guess = f80_div(f80_add(guess, f80_div(x, guess)), two);
+    } while (!f80_eq(guess, old_guess) && i++ < 100);
+    return guess;
+}
diff --git a/emu/float80.h b/emu/float80.h
@@ -49,5 +49,6 @@ extern __thread enum f80_rounding_mode f80_rounding_mode;
 #define F80_INF ((float80) {.signif = 0x8000000000000000, .exp = 0x7fff, .sign = 0})
 
 float80 f80_log2(float80 x);
+float80 f80_sqrt(float80 x);
 
 #endif
diff --git a/emu/fpu.c b/emu/fpu.c
@@ -90,6 +90,10 @@ void fpu_rndint(struct cpu_state *cpu) {
     ST(0) = f80_from_int(f80_to_int(ST(0)));
 }
 
+void fpu_sqrt(struct cpu_state *cpu) {
+    ST(0) = f80_sqrt(ST(0));
+}
+
 void fpu_yl2x(struct cpu_state *cpu) {
     ST(1) = f80_mul(ST(1), f80_log2(ST(0)));
     fpu_pop(cpu);

diff --git a/emu/fpu.h b/emu/fpu.h
@@ -49,6 +49,7 @@ void fpu_prem(struct cpu_state *cpu);
 void fpu_rndint(struct cpu_state *cpu);
 void fpu_abs(struct cpu_state *cpu);
 void fpu_chs(struct cpu_state *cpu);
+void fpu_sqrt(struct cpu_state *cpu);
 void fpu_yl2x(struct cpu_state *cpu);
 void fpu_2xm1(struct cpu_state *cpu);
 

diff --git a/emu/interp/fpu.h b/emu/interp/fpu.h
@@ -80,6 +80,7 @@
 #define FRNDINT() UNDEFINED
 #define FYL2X() UNDEFINED
 #define F2XM1() UNDEFINED
+#define FSQRT() UNDEFINED
 
 #define FUCOMI() \
     cpu->zf = f80_eq(ST(0), ST_i); \

diff --git a/jit/gen.c b/jit/gen.c
@@ -377,6 +377,7 @@ static inline bool gen_op(struct gen_state *state, gadget_t *gadgets, enum arg a
 #define FLDC(what) hh(fpu_ldc, fconst_##what)
 #define FPREM() h(fpu_prem)
 #define FRNDINT() h(fpu_rndint)
+#define FSQRT() h(fpu_sqrt)
 #define FYL2X() h(fpu_yl2x)
 #define F2XM1() h(fpu_2xm1)
 #define FSTSW(dst) if (arg_##dst == arg_reg_a) g(fstsw_ax); else UNDEFINED