strconv: reject overflow before arithmetic

lib/strconv/ftos_test.ww

@@ -14,7 +14,6 @@
 package strconv_test;
 
 import strconv;
-import os;
 import math;
 
 
@@ -43,6 +42,15 @@ fn rt64(x: f64) bool = {
 	return false;
 };
 
+fn rt32(x: f32) bool = {
+	match (stof32(f32tos(x), base.DEC)) {
+	case let v: f32 => { return math.f32bits(v) == math.f32bits(x); };
+	case let e: invalid => { return false; };
+	case let e: overflow => { return false; };
+	};
+	return false;
+};
+
 // ftos_test.ha:57-64 (G/void/NONE-equivalent) — fixed-point renders.
 @test fn f64tos_fixed() void = {
 	assert(!(!chk(13.37, "13.37")));
@@ -136,6 +144,16 @@ fn chkf32(n: f32, want: str) bool = {
 	assert(!(!chkf32(maxnorm, "3.4028235e38")));
 };
 
+@test fn f32_roundtrip_boundaries() void = {
+	assert(!(!rt32(math.f32frombits(0x00000001u32))));
+	assert(!(!rt32(math.f32frombits(0x007FFFFFu32))));
+	assert(!(!rt32(math.f32frombits(0x00800000u32))));
+	assert(!(!rt32(math.f32frombits(0x00800001u32))));
+	assert(!(!rt32(math.f32frombits(0x7F7FFFFFu32))));
+	assert(!(!rt32(math.f32frombits(0x807FFFFFu32))));
+	assert(!(!rt32(math.f32frombits(0x80800000u32))));
+};
+
 // ftos_test.ha:11/15/26 — zero, ±infinity, nan (f32 bit patterns).
 @test fn f32tos_special() void = {
 	assert(!(!chkf32(0.0f32, "0")));
@@ -162,6 +180,10 @@ fn chkf32(n: f32, want: str) bool = {
 	assert(!(!rt64(90071992547409915.0)));	// 17-digit halfway pair
 	assert(!(!rt64(90071992547409925.0)));
 	assert(!(!rt64(math.f64frombits(0x0000000000000001u64))));	// F64_MIN_SUBNORMAL (5e-324)
+	assert(!(!rt64(math.f64frombits(0x000FFFFFFFFFFFFFu64))));	// F64_MAX_SUBNORMAL
 	assert(!(!rt64(math.f64frombits(0x0010000000000000u64))));	// F64_MIN_NORMAL
+	assert(!(!rt64(math.f64frombits(0x0010000000000001u64))));	// next normal
+	assert(!(!rt64(math.f64frombits(0x800FFFFFFFFFFFFFu64))));	// negative max subnormal
+	assert(!(!rt64(math.f64frombits(0x8010000000000000u64))));	// negative min normal
 	assert(!(!rt64(math.f64frombits(0x7FEFFFFFFFFFFFFFu64))));	// F64_MAX_NORMAL
 };